Articoli di riviste: "Space radiations"

1

Gillespie, Rosemary G., Gordon M. Bennett, Luc De Meester, Jeffrey L. Feder, Robert C. Fleischer, Luke J. Harmon, Andrew P. Hendry et al. "Comparing Adaptive Radiations Across Space, Time, and Taxa". Journal of Heredity 111, n. 1 (gennaio 2020): 1–20. http://dx.doi.org/10.1093/jhered/esz064.

Testo completo

Abstract (sommario):

Abstract Adaptive radiation plays a fundamental role in our understanding of the evolutionary process. However, the concept has provoked strong and differing opinions concerning its definition and nature among researchers studying a wide diversity of systems. Here, we take a broad view of what constitutes an adaptive radiation, and seek to find commonalities among disparate examples, ranging from plants to invertebrate and vertebrate animals, and remote islands to lakes and continents, to better understand processes shared across adaptive radiations. We surveyed many groups to evaluate factors considered important in a large variety of species radiations. In each of these studies, ecological opportunity of some form is identified as a prerequisite for adaptive radiation. However, evolvability, which can be enhanced by hybridization between distantly related species, may play a role in seeding entire radiations. Within radiations, the processes that lead to speciation depend largely on (1) whether the primary drivers of ecological shifts are (a) external to the membership of the radiation itself (mostly divergent or disruptive ecological selection) or (b) due to competition within the radiation membership (interactions among members) subsequent to reproductive isolation in similar environments, and (2) the extent and timing of admixture. These differences translate into different patterns of species accumulation and subsequent patterns of diversity across an adaptive radiation. Adaptive radiations occur in an extraordinary diversity of different ways, and continue to provide rich data for a better understanding of the diversification of life.

Gli stili APA, Harvard, Vancouver, ISO e altri

2

Liu, Dalong, Wenqin Wang e Hua Ge. "Impact of urban densification on building energy consumption". E3S Web of Conferences 172 (2020): 16001. http://dx.doi.org/10.1051/e3sconf/202017216001.

Testo completo

Abstract (sommario):

The close layout of buildings is an important cause of urban densification. It makes solar radiation and long-wave radiation being blocked, scattered, and reflected multiple times. Radiant heat is a key factor affecting building energy consumption. The formation mechanism of urban radiation field in the spaces surrounded by dense buildings was analysed. Calculation models were established for the intensity of short-wave and long-wave radiations in spaces surrounded by dense buildings. Characteristics of the radiation field in the enclosed space was analysed. Two typical cities were selected for the analysis of the impact of urban densification on building energy consumption in the hot summer and warm winter zones of China. Studies have shown that the cooling energy consumption of residential buildings in enclosed space can be reduced by 7-15% compared with open space in China's hot summer and warm winter areas. This research will lay the foundation for urban design and architectural design.

Gli stili APA, Harvard, Vancouver, ISO e altri

3

Bertolet, Alejandro, e Alejandro Carabe. "Modelling Dose Effects from Space Irradiations: Combination of High-LET and Low-LET Radiations with a Modified Microdosimetric Kinetic Model". Life 10, n. 9 (23 agosto 2020): 161. http://dx.doi.org/10.3390/life10090161.

Testo completo

Abstract (sommario):

The Microdosimetric Kinetic Model (MKM) to predict the effects of ionizing radiation on cell colonies is studied and reformulated for the case of high-linear energy transfer (LET) radiations with a low dose. When the number of radiation events happening in a subnuclear domain follows a Poisson distribution, the MKM predicts a linear-quadratic (LQ) survival curve. We show that when few events occur, as for high-LET radiations at doses lower than the mean specific energy imparted to the nucleus, zF,n, a Poisson distribution can no longer be assumed and an initial pure linear relationship between dose and survival fraction should be observed. Predictions of survival curves for combinations of high-LET and low-LET radiations are produced under two assumptions for their comparison: independent and combined action. Survival curves from previously published articles of V79 cell colonies exposed to X-rays, α particles, Ar-ions, Fe-ions, Ne-ions and mixtures of X-rays and each one of the ions are predicted according to the modified MKM. We conclude that mixtures of high-LET and low-LET radiations may enhance the effect of individual actions due to the increase of events in domains provided by the low-LET radiation. This hypothesis is only partially validated by the analyzed experiments.

Gli stili APA, Harvard, Vancouver, ISO e altri

4

Pontarp, Mikael, e Owen L. Petchey. "Ecological opportunity and predator–prey interactions: linking eco-evolutionary processes and diversification in adaptive radiations". Proceedings of the Royal Society B: Biological Sciences 285, n. 1874 (7 marzo 2018): 20172550. http://dx.doi.org/10.1098/rspb.2017.2550.

Testo completo

Abstract (sommario):

Much of life's diversity has arisen through ecological opportunity and adaptive radiations, but the mechanistic underpinning of such diversification is not fully understood. Competition and predation can affect adaptive radiations, but contrasting theoretical and empirical results show that they can both promote and interrupt diversification. A mechanistic understanding of the link between microevolutionary processes and macroevolutionary patterns is thus needed, especially in trophic communities. Here, we use a trait-based eco-evolutionary model to investigate the mechanisms linking competition, predation and adaptive radiations. By combining available micro-evolutionary theory and simulations of adaptive radiations we show that intraspecific competition is crucial for diversification as it induces disruptive selection, in particular in early phases of radiation. The diversification rate is however decreased in later phases owing to interspecific competition as niche availability, and population sizes are decreased. We provide new insight into how predation tends to have a negative effect on prey diversification through decreased population sizes, decreased disruptive selection and through the exclusion of prey from parts of niche space. The seemingly disparate effects of competition and predation on adaptive radiations, listed in the literature, may thus be acting and interacting in the same adaptive radiation at different relative strength as the radiation progresses.

Gli stili APA, Harvard, Vancouver, ISO e altri

5

Potvin, L., C. Rioux e R. J. Slobodrian. "Radiations from space: Swift charged particles and neutrons". Canadian Journal of Physics 69, n. 8-9 (1 agosto 1991): 988–93. http://dx.doi.org/10.1139/p91-156.

Testo completo

Abstract (sommario):

Galactic and solar cosmic radiations received on Earth are reviewed briefly together with a discussion of proposed new detection techniques. During transient periods associated with flares the Sun emits high intensities of energetic charged particles and radiations due to subatomic processes. Neutrons are also emitted as proven recently. They should provide a nondistorted picture of hadronic processes in the outer layers of the Sun when analyzed with a dedicated neutron spectrometer, which is described in detail.

Gli stili APA, Harvard, Vancouver, ISO e altri

6

Sankarshan, Belur Mohan, Lingaraj Adarsh, Sannathammegowda Krishnaveni, Nagarajan Sowmya, Kulkarni Shrinivasrao e Holaly Chandrashekara Shastry Manjunatha. "An investigation on polymers for shielding of cosmic radiation for lunar exploration". Radiation Protection Dosimetry 199, n. 20 (dicembre 2023): 2469–74. http://dx.doi.org/10.1093/rpd/ncad248.

Testo completo

Abstract (sommario):

Abstract In outer space, we find many types of radiations that are due to solar flares, radiation belt, cosmic rays, etc. We are fortunate enough to be protected from these radiations on the surface of the Earth, whereas in other celestial objects such as planets and satellites, without a protecting atmosphere, penetration of radiation that may be ionising or non-ionising is inevitable. Hence, studying radiation environment and its effect on such celestial objects is very important for establishing facilities such as satellites, payloads, vehicles and human exploration. For such cases, manufacturing the products with lightweight, thermally stable, flexible, mechanically durable materials is essential and needs to be studied for the radiation effect. Hence, in the present work, we have made an attempt to calculate the rate of absorbed dose in case of polymers such as Polyvinyl Chloride (PVC), polytetrafluoroethylene, Mylar, polystyrene and Zylon for the lunar radiation environment. From the literature, it is found that ions up to iron has a lion share in the ionic radiation in space. The simulations were carried out for ions from hydrogen to iron using the SRIM software with various energies. It is observed that the absorbed dose rate in the polymers increases with the increase in ion mass. Further, the study can be extended to get the information of various flexible materials for these ions from which a suitable material can be chosen for the different space applications.

Gli stili APA, Harvard, Vancouver, ISO e altri

7

Cucinotta, F. A., J. W. Wilson, J. L. Shinn, F. F. Badavi e G. D. Badhwar. "Effects of target fragmentation on evaluation of LET spectra from space radiations: Implications for space radiation protection studies". Radiation Measurements 26, n. 6 (novembre 1996): 923–34. http://dx.doi.org/10.1016/s1350-4487(96)00070-4.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Liu, Dalong, Xiaowei Jia e Wenqin Wang. "Comparative analysis of simulation of urban radiation field". MATEC Web of Conferences 282 (2019): 02026. http://dx.doi.org/10.1051/matecconf/201928202026.

Testo completo

Abstract (sommario):

In order to compare the differences between various outdoor environmental simulation software in the urban radiation field, ENVI-met, RayMan and SOLWEIG were selected as the research objects. The multiple types of urban radiation intensities that can be obtained by each software are compared, and the calculation method of types of these radiations was analyzed. Effects of underlying surface on the radiation field were simulated separately. The differences in radiation field performance simulations of three softwares were compared from several aspects such as short wave, direct radiation and reflected radiation. It is found that Rayman has the high sensitivity and fast simulation speed, but the output radiation parameters are less; ENVI-met can calculate the most radiation parameters and calculate the long-short wave radiation heat transfer process between building surfaces; the SOLWEIG can be used for simulation in large outdoor space, and has more calculated radiation parameters, but has large error. All three softwares can calculate the effect of space enclosure on direct and scattered radiation.

Gli stili APA, Harvard, Vancouver, ISO e altri

9

Van Bocxlaer, Bert. "Hierarchical structure of ecological and non-ecological processes of differentiation shaped ongoing gastropod radiation in the Malawi Basin". Proceedings of the Royal Society B: Biological Sciences 284, n. 1862 (13 settembre 2017): 20171494. http://dx.doi.org/10.1098/rspb.2017.1494.

Testo completo

Abstract (sommario):

Ecological processes, non-ecological processes or a combination of both may cause reproductive isolation and speciation, but their specific roles and potentially complex interactions in evolutionary radiations remain poorly understood, which defines a central knowledge gap at the interface of microevolution and macroevolution. Here I examine genome scans in combination with phenotypic and environmental data to disentangle how ecological and non-ecological processes contributed to population differentiation and speciation in an ongoing radiation of Lanistes gastropods from the Malawi Basin. I found a remarkable hierarchical structure of differentiation mechanisms in space and time: neutral and mutation-order processes are older and occur mainly between regions, whereas more recent adaptive processes are the main driver of genetic differentiation and reproductive isolation within regions. The strongest differentiation occurs between habitats and between regions, i.e. when ecological and non-ecological processes act synergistically. The structured occurrence of these processes based on the specific geographical setting and ecological opportunities strongly influenced the potential for evolutionary radiation. The results highlight the importance of interactions between various mechanisms of differentiation in evolutionary radiations, and suggest that non-ecological processes are important in adaptive radiations, including those of cichlids. Insight into such interactions is critical to understanding large-scale patterns of organismal diversity.

Gli stili APA, Harvard, Vancouver, ISO e altri

10

Albi, Elisabetta, Samuela Cataldi, Maristella Villani e Giuseppina Perrella. "Nuclear Phosphatidylcholine and Sphingomyelin Metabolism of Thyroid Cells Changes during Stratospheric Balloon Flight". Journal of Biomedicine and Biotechnology 2009 (2009): 1–5. http://dx.doi.org/10.1155/2009/125412.

Testo completo

Abstract (sommario):

Nuclear sphingomyelin and phosphatidylcholine metabolism is involved in the response to ultraviolet radiation treatment in different ways related to the physiological state of cells. To evaluate the effects of low levels of radiation from the stratosphere on thyroid cells, proliferating and quiescent FRTL-5 cells were flown in a stratospheric balloon (BIRBA mission). After recovery, the activity of neutral sphingomyelinase, phosphatidylcholine-specific phospholipase C, sphingomyelin synthase, and reverse sphingomyelin synthase was assayed in purified nuclei and the nuclei-free fraction. In proliferating FRTL-5, space radiation stimulate nuclear neutral sphingomyelinase and reverse sphingomyelin synthase activity, whereas phosphatidylcholine-specific phospholipase C and sphingomyelin synthase were inhibited, thus inducing sphingomyelin degradation and phosphatidylcholine synthesis. This effect was lower in quiescent cells. The possible role of nuclear lipid metabolism in the thyroid damage induced by space radiations is discussed.

Gli stili APA, Harvard, Vancouver, ISO e altri

11

Abdullah, Hasnain, Asmalia Zanal, Mohamad Hakim Ahya Ilmudin, Mohd Nasir Taib, Juliana Md Sharif, Mohamad Khairul Nizam Malek, Rohaiza Baharudin, Ida Rahayu Mohamed Noordin e Ahmad Rashidy Razali. "Characteristic Evaluation of Multiple Layers Microwave Absorber Coated with Biomass Composite". Applied Mechanics and Materials 850 (agosto 2016): 88–92. http://dx.doi.org/10.4028/www.scientific.net/amm.850.88.

Testo completo

Abstract (sommario):

Radiation Absorbing Material (RAM) is used to absorb radiations of electromagnetic wave surrounding us. Thus, the multiple layers’ microwave absorber using biomass composite materials could be one of the solutions to address the problem. In order to effectively absorb the radiation of electromagnetic wave, the multiple layers’ absorber is characterized to optimize the performance of the absorber. The characterization is made by varying biomass composite material contents, thickness and other possible considerations. CST Microwave Studio software is first used to design and simulate the multiple layers’ absorber to estimate its performance. Development of multiple layers’ prototype is carried out to test its performance at free space environment. Free space dielectric measurement method is used to determine the value of multiple layers’ absorber dielectric. The dielectric value is then used in CST software in order to make the simulation more precise. Free space arch which is connected to Agilent Analyzer is used to measure absorption of multiple layers’ microwave absorber.

Gli stili APA, Harvard, Vancouver, ISO e altri

12

ZHANG, BAOCHENG, QING-YU CAI, MING-SHENG ZHAN e LI YOU. "INFORMATION CONSERVATION IS FUNDAMENTAL: RECOVERING THE LOST INFORMATION IN HAWKING RADIATION". International Journal of Modern Physics D 22, n. 12 (ottobre 2013): 1341014. http://dx.doi.org/10.1142/s0218271813410149.

Testo completo

Abstract (sommario):

In both classical and quantum world, information cannot appear or disappear. This fundamental principle, however, is questioned for a black hole, by the acclaimed "information loss paradox." Based on the conservation laws of energy, charge, and angular momentum, we recently show the total information encoded in the correlations among Hawking radiations equals exactly to the same amount previously considered lost, assuming the nonthermal spectrum of Parikh and Wilczek. Thus the information loss paradox can be falsified through experiments by detecting correlations, for instance, through measuring the covariances of Hawking radiations from black holes, such as the manmade ones speculated to appear in LHC experiments. The affirmation of information conservation in Hawking radiation will shine new light on the unification of gravity with quantum mechanics.

Gli stili APA, Harvard, Vancouver, ISO e altri

13

Blakely, Eleanor A. "The 20th Gray lecture 2019: health and heavy ions". British Journal of Radiology 93, n. 1115 (1 novembre 2020): 20200172. http://dx.doi.org/10.1259/bjr.20200172.

Testo completo

Abstract (sommario):

Objective Particle radiobiology has contributed new understanding of radiation safety and underlying mechanisms of action to radiation oncology for the treatment of cancer, and to planning of radiation protection for space travel. This manuscript will highlight the significance of precise physical and biologically effective dosimetry to this translational research for the benefit of human health. This review provides a brief snapshot of the evolving scientific basis for, and the complex current global status, and remaining challenges of hadron therapy for the treatment of cancer. The need for particle radiobiology for risk planning in return missions to the Moon, and exploratory deep-space missions to Mars and beyond are also discussed. Methods Key lessons learned are summarized from an impressive collective literature published by an international cadre of multidisciplinary experts in particle physics, radiation chemistry, medical physics of imaging and treatment planning, molecular, cellular, tissue radiobiology, biology of microgravity and other stressors, theoretical modeling of biophysical data, and clinical results with accelerator-produced particle beams. Results Research pioneers, many of whom were Nobel laureates, led the world in the discovery of ionizing radiations originating from the Earth and the Cosmos. Six radiation pioneers led the way to hadron therapy and the study of charged particles encountered in outer space travel. Worldwide about 250,000 patients have been treated for cancer, or other lesions such as arteriovenous malformations in the brain between 1954 and 2019 with charged particle radiotherapy, also known as hadron therapy. The majority of these patients (213,000) were treated with proton beams, but approximately 32,000 were treated with carbon ion radiotherapy. There are 3500 patients who have been treated with helium, pions, neon or other ions. There are currently 82 facilities operating to provide ion beam clinical treatments. Of these, only 13 facilities located in Asia and Europe are providing carbon ion beams for preclinical, clinical, and space research. There are also numerous particle physics accelerators worldwide capable of producing ion beams for research, but not currently focused on treating patients with ion beam therapy but are potentially available for preclinical and space research. Approximately, more than 550 individuals have traveled into Lower Earth Orbit (LEO) and beyond and returned to Earth. Conclusion Charged particle therapy with controlled beams of protons and carbon ions have significantly impacted targeted cancer therapy, eradicated tumors while sparing normal tissue toxicities, and reduced human suffering. These modalities still require further optimization and technical refinements to reduce cost but should be made available to everyone in need worldwide. The exploration of our Universe in space travel poses the potential risk of exposure to uncontrolled charged particles. However, approaches to shield and provide countermeasures to these potential radiation hazards in LEO have allowed an amazing number of discoveries currently without significant life-threatening medical consequences. More basic research with components of the Galactic Cosmic Radiation field are still required to assure safety involving space radiations and combined stressors with microgravity for exploratory deep space travel. Advances in knowledge The collective knowledge garnered from the wealth of available published evidence obtained prior to particle radiation therapy, or to space flight, and the additional data gleaned from implementing both endeavors has provided many opportunities for heavy ions to promote human health.

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Mitrikas, V. G. "SOME ASPECTS OF THE RADIATION EXPOSURE OF COSMONAUTS TRAVERSING THE EARTH'S MAGNETOSPHERE". Aerospace and Environmental Medicine 55, n. 3 (2021): 51–56. http://dx.doi.org/10.21687/0233-528x-2021-55-3-51-56.

Testo completo

Abstract (sommario):

Dose loading of cosmonaut's representative body organs beyond the Earth's magnetosphere was calculated for various scenarios of departure from a reference orbit in space vehicles of different design. Calculation of contribution to the equivalent doses from protons and electrons of Earth's radiations belts and galactic cosmic rays (GCR) demonstrated that, irrespective of vehicle design, during solar minimum and growing activity the equivalent dose does not exceed the established limit for a single exposure to 150 mSv. However, radiation exposure may vary in times depending on the traverse trajectory.

Gli stili APA, Harvard, Vancouver, ISO e altri

15

Suzuki, Masao, Yukio Uchihori, Hisashi Kitamura, Masakazu Oikawa e Teruaki Konishi. "Biologic Impact of Different Ultra-Low-Fluence Irradiations in Human Fibroblasts". Life 10, n. 8 (18 agosto 2020): 154. http://dx.doi.org/10.3390/life10080154.

Testo completo

Abstract (sommario):

In this study, we aimed to evaluate the cellular response of healthy human fibroblasts induced by different types of ultra-low-fluence radiations, including gamma rays, neutrons and high linear energy transfer (LET) heavy ions. NB1RGB cells were pretreated with ultra-low-fluence radiations (~0.1 cGy/7–8 h) of 137Cs gamma rays, 241Am–Be neutrons, helium, carbon and iron ions before being exposed to an X-ray-challenging dose (1.5 Gy). Helium (LET = 2.3 keV/µm), carbon (LET = 13.3 keV/µm) and iron (LET = 200 keV/µm) ions were generated with the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. No differences in cell death—measured by colony-forming assay—were observed regardless of the radiation type applied. In contrast, mutation frequency, which was detected through cell transformation into 6-thioguanine resistant clones, was 1.9 and 4.0 times higher in cells pretreated with helium and carbon ions, respectively, compared to cells exposed to X-ray-challenging dose alone. Moreover, cells pretreated with iron ions or gamma-rays showed a mutation frequency similar to cells exposed to X-ray-challenging dose alone, while cells pretreated with neutrons had 0.15 times less mutations. These results show that cellular responses triggered by ultra-low-fluence irradiations are radiation-quality dependent. Altogether, this study shows that ultra-low-fluence irradiations with the same level as those reported in the International Space Station are capable of inducing different cellular responses, including radio-adaptive responses triggered by neutrons and genomic instability mediated by high-LET heavy ions, while electromagnetic radiations (gamma rays) seem to have no biologic impact.

Gli stili APA, Harvard, Vancouver, ISO e altri

16

Ing, H., T. McLean, R. Noulty e A. Mortimer. "Bubble Detectors and the Assessment of Biological Risk from Space Radiations". Radiation Protection Dosimetry 65, n. 1 (1 giugno 1996): 421–24. http://dx.doi.org/10.1093/oxfordjournals.rpd.a031677.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Belyaev, B. I., Yu V. Belyaev, V. V. Veller, L. V. Katkovskii, É. I. Nesterovich e V. A. Sosenko. "Space Videophotometric System for Recording Optical Radiations in the Earth Atmosphere". Journal of Applied Spectroscopy 70, n. 5 (settembre 2003): 770–81. http://dx.doi.org/10.1023/b:japs.0000008877.53018.df.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

18

Frederickson, A. R., E. G. Holeman e E. G. Mullen. "Characteristics of spontaneous electrical discharging of various insulators in space radiations". IEEE Transactions on Nuclear Science 39, n. 6 (1992): 1773–82. http://dx.doi.org/10.1109/23.211366.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

19

Petrov, V. M. "Overview on experience to date on human exposure to space radiations". Advances in Space Research 14, n. 10 (ottobre 1994): 397–408. http://dx.doi.org/10.1016/0273-1177(94)90493-6.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

20

Takahashi, Akihisa, Xiaoming Su, Hiromi Suzuki, Katsunori Omori, Masaya Seki, Toko Hashizume, Toru Shimazu, Noriaki Ishioka, Toshiyasu Iwasaki e Takeo Ohnishi. "p53-Dependent Adaptive Responses in Human Cells Exposed to Space Radiations". International Journal of Radiation Oncology*Biology*Physics 78, n. 4 (novembre 2010): 1171–76. http://dx.doi.org/10.1016/j.ijrobp.2010.04.062.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

21

Cheong, Patrick Chi-Kit, Harry Ho-Yin Ng, Alan Tsz-Lok Lam e Tjonnie Guang Feng Li. "General-relativistic Radiation Transport Scheme in Gmunu. I. Implementation of Two-moment-based Multifrequency Radiative Transfer and Code Tests". Astrophysical Journal Supplement Series 267, n. 2 (1 agosto 2023): 38. http://dx.doi.org/10.3847/1538-4365/acd931.

Testo completo

Abstract (sommario):

Abstract We present the implementation of a two-moment-based general-relativistic multigroup radiation transport module in the General-relativistic multigrid numerical (Gmunu) code. On top of solving the general-relativistic magnetohydrodynamics and the Einstein equations with conformally flat approximations, the code solves the evolution equations of the zeroth- and first-order moments of the radiations in the Eulerian-frame. An analytic closure relation is used to obtain the higher order moments and close the system. The finite-volume discretization has been adopted for the radiation moments. The advection in spatial space and frequency-space are handled explicitly. In addition, the radiation–matter interaction terms, which are very stiff in the optically thick region, are solved implicitly. The implicit–explicit Runge–Kutta schemes are adopted for time integration. We test the implementation with a number of numerical benchmarks from frequency-integrated to frequency-dependent cases. Furthermore, we also illustrate the astrophysical applications in hot neutron star and core-collapse supernovae modelings, and compare with other neutrino transport codes.

Gli stili APA, Harvard, Vancouver, ISO e altri

22

Ursu, Ioan, Daniela Enciu e Adrian Toader. "Towards structural health monitoring of space vehicles". Aircraft Engineering and Aerospace Technology 89, n. 6 (2 ottobre 2017): 920–27. http://dx.doi.org/10.1108/aeat-07-2015-0173.

Testo completo

Abstract (sommario):

Purpose The purpose of this paper is to report the results of a recent project of complex tests on the survival of structural health monitoring (SHM) technology with piezo wafer active sensors (PWAS) and electromechanical impedance spectroscopy (EMIS) at simulating the concomitant action of harsh conditions of outer space: extreme temperatures, radiations, vacuum. Design/methodology/approach The tests were conducted on PWAS, consists in adhesive and aluminium discs as structural specimens, with PWAS bonded on them. The substantiating of PWAS-EMIS-based SHM technique consists the fact that real part of the PWAS electromechanical impedance spectrum follows with fidelity the resonance behaviour of the structure vibrating under the PWAS excitation. This EMIS signature is very sensitive to any structural changes and, on this basis, can be monitored the onset and progress of structural damages such as fatigue, cracks, corrosion, etc. Findings The conclusion of the tests is that the cumulative impact of severe conditions of temperature, radiation and vacuum has not generated decommissioning of sensors or adhesive, which would have meant the compromise of the methodology. A second important outcome is linked to the capability of this methodology to distinguish between the damages of mechanical origin and the false ones, caused by environmental conditions, which are, basically, harmless. Originality/value The question of transfer of PWAS-EMIS-based SHM technology to space vehicles and applications received, as a novelty, a first and encouraging response.

Gli stili APA, Harvard, Vancouver, ISO e altri

23

Bogatyrev, Yu V., D. A. Aharodnikau, S. B. Lastovsky, A. V. Ket’ko, M. M. Krechko, S. V. Shpakovsky, P. V. Rubanov, G. A. Protopopov e P. A. Chubunov. "Influence of ionizing radiation on the parameters of p-channel MOS transistors". Proceedings of the National Academy of Sciences of Belarus, Physical-Technical Series 67, n. 4 (2 gennaio 2023): 402–8. http://dx.doi.org/10.29235/1561-8358-2022-67-4-402-408.

Testo completo

Abstract (sommario):

The results of experimental studies of the influence of gamma radiation Co60 on the basic parameters of silicon epitaxial-planar p-channel MOSFET transistors under different electrical modes are presented. Transistors were manufactured according to radiation-resistant DMOS technology with design standards of 1.4 μm. As a result of transistor studies, it was established that the values of all basic parameters after the radiation dose D = 106 rads (SiO2) in active electrical irradiation modes remained within the limits of the performance criteria; the parameter, most sensitive to influence of a dose of irradiation by gamma-quanta is the threshold voltage; in the passive electrical irradiation mode the transistor’s radiations resistance in all parameters corresponds to a dose of 2,8·106 rads (SiO2). A sufficiently high radiation resistance of the studied p-channel MOSFETs makes it possible to recommend them for use in aviation and space equipment. The different degrees of radiation degradation of the studied parameters during irradiation are due to their dependence either on the effects of ionization in the layers of sub-gate and insulating dielectrics, or structural damage in the bulk silicon of the transistor active regions. The high radiation resistance of the studied p-channel MOSFETs allows recommending them for use in aviation and space equipment.

Gli stili APA, Harvard, Vancouver, ISO e altri

24

Yi, Soyeon, Soyeon Kim e Jeeyeon Song. "Analysis of the Effect of Space Radiations on the Nematode, <i> Caenorhabditis elegans </i>, through the Simulated Space Radiation". International Journal of Astronomy and Astrophysics 03, n. 03 (2013): 291–302. http://dx.doi.org/10.4236/ijaa.2013.33035.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

25

Lorion, Julien, Steffen Kiel, Baptiste Faure, Masaru Kawato, Simon Y. W. Ho, Bruce Marshall, Shinji Tsuchida, Jun-Ichi Miyazaki e Yoshihiro Fujiwara. "Adaptive radiation of chemosymbiotic deep-sea mussels". Proceedings of the Royal Society B: Biological Sciences 280, n. 1770 (7 novembre 2013): 20131243. http://dx.doi.org/10.1098/rspb.2013.1243.

Testo completo

Abstract (sommario):

Adaptive radiations present fascinating opportunities for studying the evolutionary process. Most cases come from isolated lakes or islands, where unoccupied ecological space is filled through novel adaptations. Here, we describe an unusual example of an adaptive radiation: symbiotic mussels that colonized island-like chemosynthetic environments such as hydrothermal vents, cold seeps and sunken organic substrates on the vast deep-sea floor. Our time-calibrated molecular phylogeny suggests that the group originated and acquired sulfur-oxidizing symbionts in the Late Cretaceous, possibly while inhabiting organic substrates and long before its major radiation in the Middle Eocene to Early Oligocene. The first appearance of intracellular and methanotrophic symbionts was detected only after this major radiation. Thus, contrary to expectations, the major radiation may have not been triggered by the evolution of novel types of symbioses. We hypothesize that environmental factors, such as increased habitat availability and/or increased dispersal capabilities, sparked the radiation. Intracellular and methanotrophic symbionts were acquired in several independent lineages and marked the onset of a second wave of diversification at vents and seeps. Changes in habitat type resulted in adaptive trends in shell lengths (related to the availability of space and energy, and physiological trade-offs) and in the successive colonization of greater water depths.

Gli stili APA, Harvard, Vancouver, ISO e altri

26

Hossain, M. Ilias. "Hawking Non-thermal and Purely Thermal Radiations of Rotating Black Hole in Anti-de Sitter Space Time by Hamilton-Jacobi Method". GANIT: Journal of Bangladesh Mathematical Society 37 (20 febbraio 2018): 99–109. http://dx.doi.org/10.3329/ganit.v37i0.35729.

Testo completo

Abstract (sommario):

We have explored Hawking non-thermal and purely thermal radiations of Kerr-anti-de Sitter (KAdS) black hole using massive particles tunneling method by taking into account the space time background as dynamical, energy and angular momentum as conserved incorporating the selfgravitation effect of the emitted particles. The results we have obtained for KAdS black hole have shown that the tunneling rates are related to the change of Bekenstein-Hawking entropy and the derived emission spectrum deviates from the pure thermal spectrum and also the obtaining results for KAdS black hole are accordant with Parikh and Wilczek’s opinion and gives a correction to the Hawking radiation of KAdS black hole.GANIT J. Bangladesh Math. Soc.Vol. 37 (2017) 99-109

Gli stili APA, Harvard, Vancouver, ISO e altri

27

HSU, JONG-PING. "YANG–MILLS GRAVITY IN FLAT SPACE–TIME II: GRAVITATIONAL RADIATIONS AND LEE–YANG FORCE FOR ACCELERATED COSMIC EXPANSION". International Journal of Modern Physics A 24, n. 28n29 (20 novembre 2009): 5217–33. http://dx.doi.org/10.1142/s0217751x0904765x.

Testo completo

Abstract (sommario):

Within Yang–Mills gravity with translation group T(4) in flat space–time, the invariant action involving quadratic translation gauge-curvature leads to quadrupole radiations, which are shown to be consistent with experiments. The radiation power turns out to be the same as that in Einstein's gravity to the second-order approximation. We also discuss an interesting physical reason for the accelerated cosmic expansion based on the long-range Lee–Yang force of Ub(1) gauge field associated with the established conservation law of baryon number. We show that the Lee–Yang force can be related to a linear potential ∝ r, provided the gauge field satisfies a fourth-order differential equation in flat space–time. Furthermore, we consider an experimental test of the Lee–Yang force related to the accelerated cosmic expansion. The necessity of generalizing Lorentz transformations for accelerated frames of reference and accelerated Wu–Doppler effects are briefly discussed.

Gli stili APA, Harvard, Vancouver, ISO e altri

28

OO, Myo, Nahrul Rashid, Julia Karim, Zin Mohamed, Rosminazuin Rahim, Amelia Azman e Nurul Hasbullah. "Electrical characterization of commercial NPN bipolar junction transistors under neutron and gamma irradiation". Nuclear Technology and Radiation Protection 29, n. 1 (2014): 46–52. http://dx.doi.org/10.2298/ntrp1401046o.

Testo completo

Abstract (sommario):

Electronics components such as bipolar junction transistors, diodes, etc. which are used in deep space mission are required to be tolerant to extensive exposure to energetic neutrons and ionizing radiation. This paper examines neutron radiation with pneumatic transfer system of TRIGA Mark-II reactor at the Malaysian Nuclear Agency. The effects of the gamma radiation from Co-60 on silicon NPN bipolar junction transistors is also be examined. Analyses on irradiated transistors were performed in terms of the electrical characteristics such as current gain, collector current and base current. Experimental results showed that the current gain on the devices degraded significantly after neutron and gamma radiations. Neutron radiation can cause displacement damage in the bulk layer of the transistor structure and gamma radiation can induce ionizing damage in the oxide layer of emitter-base depletion layer. The current gain degradation is believed to be governed by the increasing recombination current in the base-emitter depletion region.

Gli stili APA, Harvard, Vancouver, ISO e altri

29

Held, Kathryn D. "Effects of low fluences of radiations found in space on cellular systems". International Journal of Radiation Biology 85, n. 5 (gennaio 2009): 379–90. http://dx.doi.org/10.1080/09553000902838558.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

30

INCERTI, S., G. BALDACCHINO, M. BERNAL, R. CAPRA, C. CHAMPION, Z. FRANCIS, P. GUÈYE et al. "THE GEANT4-DNA PROJECT". International Journal of Modeling, Simulation, and Scientific Computing 01, n. 02 (giugno 2010): 157–78. http://dx.doi.org/10.1142/s1793962310000122.

Testo completo

Abstract (sommario):

The Geant4-DNA project proposes to develop an open-source simulation software based and fully included in the general-purpose Geant4 Monte-Carlo simulation toolkit. The main objective of this software is to simulate biological damages induced by ionizing radiations at the cellular and sub-cellular scale. This project was originally initiated by the European Space Agency for the prediction of the deleterious effects of radiations that may affect astronauts during future long duration space exploration missions. In this paper, the Geant4-DNA collaboration presents an overview of the whole on-going project, including its most recent developments that are available in the Geant4 toolkit since December 2009 (release 9.3), as well as an illustration example simulating the direct irradiation of a biological chromatin fiber. Expected extensions involving several research domains, such as particle physics, chemistry and cellular and molecular biology, within a fully interdisciplinary activity of the Geant4 collaboration are also discussed.

Gli stili APA, Harvard, Vancouver, ISO e altri

31

Nayak, Jagannath, e Deepak Kumar. "A Review on Thermophotovoltaic Energy Conversions and its Space Power Applications". Journal of Physics: Conference Series 2603, n. 1 (1 ottobre 2023): 012011. http://dx.doi.org/10.1088/1742-6596/2603/1/012011.

Testo completo

Abstract (sommario):

Abstract Thermophotovoltaic (TPV) system coverts heat radiations from various sources like Thermophotovoltaic (TPV) system coverts heat radiations from various sources like combustion of fuels, industrial waste heat and nuclear energy into electricity. To fulfil the demand of energy TPV is an alternate, can enable approaches to energy storage and conversion. The TPV model consists of multiple arrays of TPV cells, an emitter, a radiator and a filter. one of the important advantages of TPVs are the high efficiencies and direct conversion of DC power. This paper presents the research being conducted till date in the field of Thermophotovoltaic cell and space applications of TPV cells. We have Thermophotovoltaic has been regarded as an energy substitute in radioisotope deep space power system for thermoelectric. TPV provides outstanding potential improvement in mass specific power as well as in efficiency. TPV system also proposed for inner planetary solar system. This idea leads TPV capability to store energy in the form of heat energy rather than electrical energies which is common in photovoltaic system. The current effort to derive the demonstration of efficiency conversion up to 19% and it enhances the specific power W/kg at the system level. Next generation TPV concepts are also reviewed in order to explore the future space power application. The application of TPV that includes radioisotope Thermophotovoltaic (RTPV) and solar Thermophotovoltaic (STPV) plays a vital role in deep space powered systems.

Gli stili APA, Harvard, Vancouver, ISO e altri

32

Skipwith, Phillip L., e Paul M. Oliver. "Ecologically diverse island-associated lizard radiation shows idiosyncratic trait diversification shifts and homogenous speciation dynamics". Evolution 77, n. 1 (8 dicembre 2022): 138–54. http://dx.doi.org/10.1093/evolut/qpac002.

Testo completo

Abstract (sommario):

Abstract A key area of interest in evolutionary biology has been understanding the role of ecological opportunity in the formation of adaptive radiations, lineages where speciation and phenotypic diversification are driven by open ecological opportunity. Evolutionary theory posits that adaptive radiations should show initial bursts of ecomorphological diversification and rapid speciation, and that these two processes are correlated. Here, we investigate and contrast these predictions across ecomorphologically diverse continental (Australia) and insular (New Caledonia and New Zealand) radiations of diplodactyloid geckos. We test two key hypotheses: (a) that island colonization and the transition to novel niche-space has resulted in increased rates of speciation and trait diversification and (b) that rates of morphological diversification are correlated across multiple trait axes. Surprisingly, we find that speciation rate is homogenous and morphological diversification rates are idiosyncratic and uncorrelated with speciation rates. Tests of morphological integration suggests that while all traits coevolve, constraint may act differentially on individual axes. This accords with a growing number of studies indicating that ecologically diverse and species-rich radiations can show limited or no evidence of exceptional regime shifts in speciation dynamics or morphological diversification, especially in continental contexts.

Gli stili APA, Harvard, Vancouver, ISO e altri

33

Abdul Amir, Haider F., e Fuei Pien Chee. "Evaluation on Diffusion of Bipolar Junction Transistor (BJT) Charge-Carrier and its Dependency on Total Dose Irradiation". Advanced Materials Research 701 (maggio 2013): 71–76. http://dx.doi.org/10.4028/www.scientific.net/amr.701.71.

Testo completo

Abstract (sommario):

Electronic device that subjected to various effects by radiations can cause small interferences such as noises in the circuit. These effects are especially critical in operating environment such as outer space, where radiation comes in stronger and more frequent. In this research, analytical study on the effects of ionizing radiation induced by 60Co gamma (γ) rays in bipolar junction transistor (BJT) devices had been performed. It was found that the high energy of the radiation allows more valence electrons to be excited to the conduction band in the BJT. This leads to the production of a large number of excited atoms and increases the holes in the valence band. The increase of holes in the base region due to trapping will increase the probability of recombination and reducing the number of electrons that reaches the collector region. This ionizing radiation effect was found to arouse either a permanent or temporarily damage in the devices depending on their current drives and total dose absorbed.

Gli stili APA, Harvard, Vancouver, ISO e altri

34

Volk, Kevin, e Sun Kwok. "A self-consistent photoionization-dust continuum-molecular line transfer model of NGC7027". Symposium - International Astronomical Union 180 (1997): 285. http://dx.doi.org/10.1017/s007418090013102x.

Testo completo

Abstract (sommario):

A model to simulate the entire spectrum (1000 Å to 1 cm) of the high-excitation young planetary nebula NGC 7027 is presented. The ionized, dust, and molecular components of the object are modeled using geometric parameters obtained from visible, radio, infrared, and CO data. The physical processes considered include recombination lines of H and He, collisional excited lines of metals, bf and ff continuum radiations, two-photon radiation, dust continuum radiation, and molecular rotational and vibrational transitions. The dust component is assumed to be heated by a combination of direct starlight and the line and continuum radiation from the ionized nebula. The molecular component of the nebula is coupled to the dust component through the stimulated absorption of the dust continuum radiation. Specifically, we compare the predicted fluxes of the CO rotational lines and the 179.5 μm water rotational line to those observed by the Infrared Space Observatory satellite (Liu et al. 1996, A&A in press).

Gli stili APA, Harvard, Vancouver, ISO e altri

35

Capolupo, Antonio. "Dark Matter and Dark Energy Induced by Condensates". Advances in High Energy Physics 2016 (2016): 1–10. http://dx.doi.org/10.1155/2016/8089142.

Testo completo

Abstract (sommario):

It is shown that the vacuum condensate induced by many phenomena behaves as a perfect fluid which, under particular conditions, has zero or negative pressure. In particular, the condensates of thermal states of fields in curved space and of mixed particles have been analyzed. It is shown that the thermal states with the cosmic microwave radiation temperature and the Unruh and the Hawking radiations give negligible contributions to the critical energy density of the universe, while the thermal vacuum of the intercluster medium could contribute to the dark matter, together with the vacuum energy of fields in curved space-time and of mixed neutrinos. Moreover, a component of the dark energy can be represented by the vacuum of axion-like particles mixed with photons and superpartners of neutrinos. The formal analogy among the systems characterized by the condensates can open new scenarios in the possibility of detecting the dark components of the universe in table top experiments.

Gli stili APA, Harvard, Vancouver, ISO e altri

36

Nawaz, Faisal, Bulbul Jan, Faisal Ahmed Khan Afridi, M. Ayub Khan Yousufzai e Faraz Mehmood. "Comparative Study of the Dynamics of Cosmic Rays for the Pakistan and China Atmospheric Regions". Journal of Mathematical and Fundamental Sciences 52, n. 3 (31 dicembre 2020): 261–75. http://dx.doi.org/10.5614/j.math.fund.sci.2020.52.3.1.

Testo completo

Abstract (sommario):

This paper presents an analysis of cosmic ray intensity in Pakistan air space using spatial interpolation, comparing it with Chinese cosmic ray records from 1984 to 1993. The Exploratory Data Analytic (EDA) approach was applied to compare the cosmic ray fluctuations in both countries. The time series plot of the monthly cosmic rays showed relatively flatter counts in Pakistan than in China. The cosmic ray data for the years 1984 to 1993 fell within Solar Cycle 22, which lasted from 1986 to 1996, with its maximum phase in 1989 to 1991. The cosmic radiation varies between the atmospheric regions of Pakistan and China due to modulations in intensity that are accessible accordingly. It can be explained by purely astrophysical phenomena: (1) the source of emission of cosmic radiation may be different, (2) the rate at which emanation takes place depends on bursts of deep space dynamical objects from their sources that may be affected by solar wind and other solar radiations. Therefore, modulations in intensity are not only due to different geophysical locations. This study will help government organizations to predict and forecast cosmic rays values.

Gli stili APA, Harvard, Vancouver, ISO e altri

37

Mohanty, Asutosh, Bikash Ranjan Behera, Karu P. Esselle, Mohammed H. Alsharif, Abu Jahid e Syed Agha Hassnain Mohsan. "Investigation of a Dual-Layer Metasurface-Inspired Fractal Antenna with Dual-Polarized/-Modes for 4G/5G Applications". Electronics 11, n. 15 (28 luglio 2022): 2371. http://dx.doi.org/10.3390/electronics11152371.

Testo completo

Abstract (sommario):

In this research article, a dual-polarized compact bow-tie-shaped irregular fractal antenna with a dual metasurface (DMS) for directional radiation applications is designed using a dual-mode simple feeding mechanism. A short-circuited strip linked between the impedance transformation feed and the radiating patch activates the induced coupling modes, which are capacitive (C-mode) and inductive (L-mode), respectively. The C-mode antenna operates at 2.39–2.53 GHz, whereas the L-mode antenna operates at 2.88–4.49 GHz. It comprises a DMS positioned at 0.22λ∘ from the antenna with 0.016λ∘ separation and a 4 × 4 array of checkerboard type hole-injected tiny unit cells on each metasurface. A rectangular cavity-backed slot was employed as the ground plane to emulsify the reflected energy waves from the DMS, in order to start the coupling process with the boresight radiation, resulting in high gain and suppressed backward radiations. The gain in C-mode was 6.74 dBi, and the gain in L-mode was 7.7 dBi. For validation, a miniaturized metasurface antenna with the overall size of 0.32λ∘ × 0.32λ∘ × 0.22λ∘ (where λ∘ is the free-space wavelength at 2.45 GHz) was fabricated and measured. The measured outcomes highlight its potential for 4G/5G wireless applications.

Gli stili APA, Harvard, Vancouver, ISO e altri

38

Singhal, Umang, e Yash Pal. "Propellant-Less Thrust Generation - A Review". Applied Mechanics and Materials 852 (settembre 2016): 639–45. http://dx.doi.org/10.4028/www.scientific.net/amm.852.639.

Testo completo

Abstract (sommario):

This paper introduces a concept of propellant-less microwave thruster for upper stage and space applications. The propellant-less microwave thruster works on classical electromagnetic theory, where the microwave radiations are converted to the electromagnetic pressure that acts as axial thrust. In microwave thrusters, microwaves are radiated to a sealed conical cavity which follows the contour of the thrusters to produce pressure. Normally, there are three types of methods by which thrust can be produced without utilizing any propellant. Cannae Drive, EmDrive, and the Wrap Drive are mostly used. The first two are based on the principle of microwave radiation, whereas the third method is just a concept in various science fiction films. The EmDrive can produce a small amount of thrust, therefore, its application is limited to upper stage thruster, orbit/trajectory correction, and deep-space exploration. This paper provides an insight on the feasibility of EmDrive for space application by comparing its performance with ion propulsion system. The proposed microwave propulsion system has low system mass (typically in Kgs), produces high thrust (in mN) and even has higher specific impulse (in years) which can outweigh the current ion propulsion system.

Gli stili APA, Harvard, Vancouver, ISO e altri

39

Mordachev, V. I. "Characteristics of the electromagnetic environment created by radiations of user equipment of ...4G/5G/6G cellular (mobile) communications in buildings". Doklady BGUIR 19, n. 6 (1 ottobre 2021): 42–50. http://dx.doi.org/10.35596/1729-7648-2021-19-6-42-50.

Testo completo

Abstract (sommario):

The goal of the work is to substantiate the technique for assessing the intensity of electromagnetic background generated by the set of radiating user devices of mobile communications in multi-storey buildings. For known empirical models of radio wave propagation in buildings, expressions are obtained for the probability distribution density and expectation of the power flux density of electromagnetic fields generated inside building by these sources from various parts of the building's interior space: from the near zone with radio wave propagation conditions similar to free space; and from the far zone, for which, along with intense attenuation of radio waves due to internal obstacles, a «quasi-waveguide» propagation of radio waves along corridors and industrial premises is also possible in certain directions. Relationships are obtained for the average levels of individual components of the electromagnetic background, determined as scalar sums of power flux density values of the fields generated by the sets of radiating devices of both the near zone and the far zone as a whole or its individual parts, characterized by different conditions of radio wave propagation. A method is proposed for assessing the electromagnetic background inside buildings based on approximation of sections of the inner surface of the premises in which the observation point is located, and the outer surface of the building, in the inner space of which radiation sources are randomly distributed, by the corresponding sections of the inner and outer spherical surfaces that are the subtend areas of the corresponding solid angles, in space elements of which a different spatial densities and radiation powers of sources and different conditions of radio wave propagation are possible. The results can be used to analyze the electromagnetic ecology of habitat and the electromagnetic safety of population at the full-scale implementation of 4G/5G/6G mobile communications, as well as to analyze the electromagnetic compatibility of systems using frequency bands for mobile communications on a primary and secondary basis.

Gli stili APA, Harvard, Vancouver, ISO e altri

40

Boudjada, Mohammed Y., Patrick H. M. Galopeau, Sami Sawas, Valery Denisenko, Konrad Schwingenschuh, Helmut Lammer, Hans U. Eichelberger, Werner Magnes e Bruno Besser. "Low-altitude frequency-banded equatorial emissions observed below the electron cyclotron frequency". Annales Geophysicae 38, n. 3 (24 giugno 2020): 765–74. http://dx.doi.org/10.5194/angeo-38-765-2020.

Testo completo

Abstract (sommario):

Abstract. The ICE (Instrument Champ Électrique) experiment on board the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite recorded frequency-banded wave emissions below the electron cyclotron frequency, with band spacing ≳ frequency low-hybrid resonance, in the vicinity of the magnetic equatorial plane. Those radiations were observed in the beginning of the year 2010 on the night side of Earth and rarely on the day side. We distinguish two components: one appears as frequency bands continuous in time between a few kilohertz and up to 50 kHz, and the other one is from 50 to 800 kHz. The first component exhibits positive and negative frequency drift rates in the Southern Hemisphere and Northern Hemisphere, at latitudes between 40 and 20∘. The second one displays multiple spaced frequency bands. Such bands mainly occur near the magnetic equatorial plane with a particular enhancement of the power level when the satellite latitude is close to the magnetic equatorial plane. We show in this study the similarities and the discrepancies between the non-free-space DEMETER frequency-banded emissions and the well-known free-space terrestrial kilometric radiation. The hollow cones of the DEMETER frequency-banded wave emissions are oriented towards Earth's ionosphere. We suggest that the source region is localized in regions poleward of the plasmapause where the ratio of the plasma frequency to gyro-frequency is smaller than one.

Gli stili APA, Harvard, Vancouver, ISO e altri

41

Curtis, S. B. "Possible effects of protracted exposure on the additivity of risks from space radiations". Advances in Space Research 18, n. 1-2 (gennaio 1996): 41–44. http://dx.doi.org/10.1016/0273-1177(95)00787-f.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

42

Rubin, Ilan N., Iaroslav Ispolatov e Michael Doebeli. "Evolution to alternative levels of stable diversity leaves areas of niche space unexplored". PLOS Computational Biology 17, n. 7 (28 luglio 2021): e1008650. http://dx.doi.org/10.1371/journal.pcbi.1008650.

Testo completo

Abstract (sommario):

One of the oldest and most persistent questions in ecology and evolution is whether natural communities tend to evolve toward saturation and maximal diversity. Robert MacArthur’s classical theory of niche packing and the theory of adaptive radiations both imply that populations will diversify and fully partition any available niche space. However, the saturation of natural populations is still very much an open area of debate and investigation. Additionally, recent evolutionary theory suggests the existence of alternative evolutionary stable states (ESSs), which implies that some stable communities may not be fully saturated. Using models with classical Lotka-Volterra ecological dynamics and three formulations of evolutionary dynamics (a model using adaptive dynamics, an individual-based model, and a partial differential equation model), we show that following an adaptive radiation, communities can often get stuck in low diversity states when limited by mutations of small phenotypic effect. These low diversity metastable states can also be maintained by limited resources and finite population sizes. When small mutations and finite populations are considered together, it is clear that despite the presence of higher-diversity stable states, natural populations are likely not fully saturating their environment and leaving potential niche space unfilled. Additionally, within-species variation can further reduce community diversity from levels predicted by models that assume species-level homogeneity.

Gli stili APA, Harvard, Vancouver, ISO e altri

43

Amir, Haider F. Abdul, e Fuei Pien Chee. "Monte Carlo Simulation of Alpha (α) Particles Penetration in Nanoscale Silicon Semiconductor Materials". Advanced Materials Research 528 (giugno 2012): 237–40. http://dx.doi.org/10.4028/www.scientific.net/amr.528.237.

Testo completo

Abstract (sommario):

Microsystems, both in space and ground level, will use systems with III-V semiconductors and devices of nanoscale. Vulnerability of this system towards the radiations warrants extra care to be taken. Therefore, appropriate test and analysis to assure the hardness (radiation resistance) of components to be used in various radiation environments is necessary. In this paper, the defect generated in the interaction of alpha (α) particles and silicon (Si) semiconductor material is simulated using SRIM (Stopping and Range of Ions in Matter). The induced defects are in the form of vacancies, defect clusters and dislocations. Besides, the defect is found influencing the kinetic processes that occur both inside and outside the cascade volume. The radiation tolerance between the conventional scale and nanoscale thickness of silicon layer is also being compared. From the findings, it is observed that when the thickness of silicon layer is scaled down, defect that induced by the energy deposition of -particles is significantly lesser. This means that nanoscale silicon layer features improved radiation robustness towards the deposition of energetic ions.

Gli stili APA, Harvard, Vancouver, ISO e altri

44

HSU, JONG-PING. "YANG–MILLS GRAVITY IN FLAT SPACE–TIME I: CLASSICAL GRAVITY WITH TRANSLATION GAUGE SYMMETRY". International Journal of Modern Physics A 21, n. 25 (10 ottobre 2006): 5119–39. http://dx.doi.org/10.1142/s0217751x06034082.

Testo completo

Abstract (sommario):

We formulate and explore the physical implications of a new translation gauge theory of gravity in flat space–time with a new Yang–Mills action, which involves quadratic gauge curvature and fermions. The theory shows that the presence of an "effective Riemann metric tensor" for the motions of classical particles and light rays is probably the manifestation of the translation gauge symmetry in flat physical space–time. In the post-Newtonian approximation of the tensor gauge field produced by the energy–momentum tensor, the results are shown to be consistent with classical tests of gravity and with the quadrupole radiations of binary pulsars.

Gli stili APA, Harvard, Vancouver, ISO e altri

45

Kwon, You Jin, e Dong Kun Lee. "Thermal Comfort and Longwave Radiation over Time in Urban Residential Complexes". Sustainability 11, n. 8 (15 aprile 2019): 2251. http://dx.doi.org/10.3390/su11082251.

Testo completo

Abstract (sommario):

Large cities with a high concentration of high-rise buildings are shaded by urban canyon. This brings a cooling effect compared to the space exposed to the sun, but is not always cool due to the longwave radiation emitted from buildings and the built environment. We tested the micro-scale effects of major external spatial factors, trees, and buildings, under shade on longwave radiation shifts to understand the effects of large shaded areas in megacities. Incoming and outgoing longwave radiations (ILR and OLR, respectively) were found to decrease the overall observation by time zone. Longwave radiation on a micro-scale was also inversely proportional to the tree volume. From mean radiant temperature (MRT) analysis, we found that about a 10% decrease in MRT could be achieved by increasing tree volume by around 50%. Larger tree volumes corresponded to greater blocking effects on longwave radiation. Considering the tree volume, a multilayer urban tree canopy composition can more favorably improve the thermal environment and energy sustainability of a city compared to a single-layer canopy. Larger trees planted with harmonious shrubs are the most effective in reducing longwave radiation.

Gli stili APA, Harvard, Vancouver, ISO e altri

46

Shoorian, Sarah, S. Amir Hosein Feghhi, Hamid Jafari e Reza Amjadifard. "Studying the effects of multi-layer shielding in reducing space radiations exposure of human and electrical components in space missions". Journal of Space Science and Technology 16, n. 2 (22 maggio 2023): 19–26. http://dx.doi.org/10.30699/jsst.2023.1422.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

47

Fujinawa, Yukio, e Kozo Takahashi. "Electromagnetic radiations associated with major earthquakes". Physics of the Earth and Planetary Interiors 105, n. 3-4 (gennaio 1998): 249–59. http://dx.doi.org/10.1016/s0031-9201(97)00117-9.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

48

Kotov, Yu D., V. N. Yurov, E. E. Lupar, K. F. Vlasik, A. I. Arkhangelsky, A. S. Glyanenko, I. V. Rubtsov, V. V. Kadilin e V. G. Tyshkevich. "The NATALYA-2M spectrometer of high-energy radiations for the CORONAS-PHOTON space project". Solar System Research 45, n. 2 (25 marzo 2011): 97–122. http://dx.doi.org/10.1134/s0038094611020080.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

49

Sprugnoli, Giulia, Yvonne D. Cagle e Emiliano Santarnecchi. "Microgravity and Cosmic Radiations During Space Exploration as a Window Into Neurodegeneration on Earth". JAMA Neurology 77, n. 2 (1 febbraio 2020): 157. http://dx.doi.org/10.1001/jamaneurol.2019.4003.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

50

El-Ouardi, Youssef, Adil Aknouch, Ahmed Dadouch, Mohammed Mouhib e Mounir Benmessaoud. "A gamma radiation exposure risk assessment using Monte Carlo simulation and an adult anthropomorphic phantom". E3S Web of Conferences 234 (2021): 00060. http://dx.doi.org/10.1051/e3sconf/202123400060.

Testo completo

Abstract (sommario):

The human body is vulnerable to exposure to ionizing radiation permanently. These radiations can be of natural origin such as soil and space, or of artificial and medical origins etc. Despite the great benefits that come from the applications of ionizing radiation in human life can turn at any time into threats to the life of the population once there is serious exposure to ionizing radiation. The aim of this work is to assess the risks of exposure by gamma radiation using the Monte Carlo simulation and an anthropomorphic phantom. This study is carried out on gamma rays received from the cobalt-60 irradiator of the National Institute of Agronomic Research (NIAR) Tangier / Morocco. With the code Geant4 we calculate the absorbed dose by the whole phantom body placed in front of the gamma irradiator inside the NIAR ionization cell. Dose calculations are made as a function of three parameters: phantom-irradiator distance, exposure time and as a function of gamma irradiator activity. The results clearly show that the dose absorbed and thus the danger of irradiation decreases by increasing the phantom-source distance, and by reducing the exposure time and the activity of the cobalt-60 source.

Gli stili APA, Harvard, Vancouver, ISO e altri

Articoli di riviste sul tema "Space radiations"

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili