Journal articles on the topic 'Twin-beam state'

We show the equivalence between two different communication schemes that employ a couple of modes of the electromagnetic field. One scheme uses unconventional heterodyne detection, with correlated signal and image band modes in a twin-beam state from parametric downconversion. The other scheme is realized through a complex-number coding over quadrature-squeezed states of two uncorrelated modes, each detected by ordinary homodyning. This equivalence concerns all the stages of the communication channel: the encoded state, the optimal amplifier for the channel, the master equation modeling the loss, and the output measurement scheme. The unitary transformation that connects the two communication schemes is realized by a frequency conversion device.

We present an experimental investigation of the spatio-spectral coherence properties of bright twin-beam states (TWBs) as functions of different parameters, such as pump mean power and tuning angle of the employed nonlinear crystal. Our attention is mainly focused on the possible relations among the different quantities under investigation. Particular attention is devoted to the evolution of the number of spatio-spectral modes describing the radiation field, as it represents an interesting property to be controlled in view of possible applications to quantum state engineering protocols.

Abstract The calculation of autocorrelation functions represents a routinely used tool to characterise quantum states of light. In this paper, we evaluate the g(2) function for detected photons in the case of mesoscopic multi-mode twin-beam states in order to fully investigate their statistical properties starting from measurable quantities. Moreover, we show that the second-order autocorrelation function is also useful to estimate the spurious effects affecting the employed Silicon-photomultiplier detectors.

ABSTRACTInSb has been considered as a promising material for spintronic applications owing to its pronounced spin effects as a result of large intrinsic electronic g-factor. In addition, embedding InSb quantum nanostructures in a GaAs matrix could create type-II band alignment, where radiation lifetimes are longer than those of the typical type-I systems. Such characteristics are promising for memory devices and infrared photonic applications. The growth of InSb/GaAs quantum nanostructures by strain driven mechanism using molecular beam epitaxy with low growth temperature, slow growth rate, Sb soaking process prior to In deposition, and small amount of In deposition typically creates a mixture of twin and single nano-stripe structures with truncated pyramid shape. In this work, we further investigate the growth mechanism of such twin InSb/GaAs nano-stripes by controlling the growth conditions, consisting of nanostructure growth duration and growth temperature. When the growth temperature is kept to less than 300°C and In deposition is set to only a few monolayers, we found that 25-40% of formed nanostructures are twin InSb/GaAs nano-stripes. However, when the In deposition is stopped immediately after the spotty reflection high-energy electron diffraction patterns are observed, the ratio of twin nano-stripes to single ones is increased to 50-60%. We therefore describe the growth mechanism of twin nano-stripes as the early state of single nano-stripe formation, where the twin nano-stripes are initially formed during the first monolayer of InSb formation as a result of large lattice mismatch of 14.6%. When In deposition is increased to a few monolayers, the gap between twin nano-stripes is filled up and consequently forms the single nano-stripes instead. With this particular twin nano-stripe growth mechanism, the preservation of high ratio of twin nano-stripe formation can be expected by further reducing the growth temperature, i.e. less than 260°C. These twin nano-stripes may find applications in the fields of spintronics and novel interference nano-devices.

AbstractThis work is concerned with comparative tests involving single-spot and twin-spot laser welding of thermomechanically rolled TRIP steel. The welding tests were carried out using keyhole welding and a solid state laser. In the case of twin-spot laser beam welding, the power distribution of beams was 50%:50%. The changes in macro- and microstructures were investigated using light and scanning electron microscopy. Three main zones subjected to the tests included the fusion zone, the heat affected zone and the intercritical heat affected zone (transition zone between the base material and the HAZ). Special attention was paid to the effect of various thermal cycles on the microstructure of each zone and on martensite morphology. The tests involved hardness measurements carried out in order to investigate the effect of different microstructures on mechanical properties of welds.

AbstractA one-dimensional variational data assimilation (1DVar) method is presented based on the depth- and time-averaged alongshore-uniform surfzone wave and current equations, for simultaneous estimation of three uncertain variables: bathymetry, incident wave boundary conditions, and bed roughness. The method is validated using twin tests and in situ field observations, and its results are shown to be comparable to those of an existing ensemble-based bathymetry inversion technique. Unlike existing techniques, the ability to simultaneously estimate boundary conditions and bed roughness along with bathymetry also means the 1DVar method can produce full state estimates without the requirement for additional supporting measurements (e.g., direct measurements of the incident waves). A proof-of-concept field application is shown using observations collected from an unmanned quadcopter sensor package that measures surfzone wave height from a fixed-beam lidar range finder, and time-averaged longshore current from particle image velocimetry of drifting surface foam.

Mn-Cu high damping alloy is a twin-type damping alloy. Owing to its martensite twin structure at room temperature, it can convert vibration energy into heat energy, thereby reducing vibration. Although essentially a nonlinear elastic material, Mn-Cu damping alloys are treated as linear elastic materials in current engineering practice. However, introducing a constant damping coefficient alone will produce significant errors when modeling vibration reduction characteristics of the material, especially under impact loading. In this study, vibration test was performed on Mn-Cu damping alloy cantilever beam subjected to an impact load and deviation between the test result and the one of existing modeling method was analyzed. A generalized fractional-order Maxwell model was established to describe the nonlinear constitutive relation of the Mn-Cu damping alloy. Then, the model was extended to the three-dimensional state and a secondary development was performed. Finally, various applications for the damping alloy were explored and the effects of the damping alloy on the vibration characteristics of composite cantilever beam structures subjected to impact loads were investigated with the aim of better understanding the dynamic characteristics and improving the effectiveness of vibration reduction applications using Mn-Cu damping alloy in the future.

We measure high-order correlation functions of detected-photon numbers in the mesoscopic regime by means of hybrid photodetectors. The analytical expressions for correlations are evaluated in terms of quantities that can be experimentally accessed by a selfconsistent analysis of the detectors' outputs. We demonstrate that high-order correlations can be used to characterize the nature of the optical states, for instance by better discriminating between classical and quantum behavior even in critical situations, such as multimode twin-beam state. The results are in very good agreement with the theory, both for classical states and quantum states.

In this work, quantum metrology techniques are applied to the imaging of objects with a nonuniform refractive spatial profile. A sensible improvement on the classical accuracy is shown to be found when the “Twin Beam (TWB) State” is used. In particular, exploiting the multimode spatial correlation, naturally produced in the Parametric Down Conversion (PDC) process, allows a 2D reconstruction of complex spatial profiles, thus enabling an enhanced imaging. The idea is to use one of the spatially multimode beams to probe the sample and the other as a reference to reduce the noise. A similar model can also be used to describe wave front distortion measurements. The model is meant to be followed by a first experimental demonstration of such enhanced measurement scheme.

We address de-Gaussification of continuous variables Gaussian states by optimal non-deterministic noiseless linear amplifier (NLA) and analyze in details the properties of the amplified states. In particular, we investigate the entanglement content and the non-Gaussian character for the class of non-Gaussian entangled state obtained by using NL-amplification of two-mode squeezed vacua (twin-beam, TWB). We show that entanglement always increases, whereas improved EPR correlations are observed only when the input TWB has low energy. We then examine a Braunstein-Kimble-like protocol for the teleportation of coherent states, and compare the performances of TWB-based teleprotation with those obtained using NL-amplified resources. We show that teleportation fidelity and security may be improved for a large range of NLA parameters (gain and threshold).

Crystalline interfaces associated with lattice translations such as stacking-faults (SFs) and twin boundaries may be characterized in the transmission electron microscope (TEM) by oscillatory fringe contrast known as SF, or rigid-body-translation, fringes. Such fringe contrast is usually obtained using weak-beam bright-field (BF) or dark-field (DF) conditions with ideally only one reflection, g, excited. The nature of the SF contrast has been explained by dynamical theory of electron diffraction in terms of the Howie-Whelan equations [1]. The fringe contrast arises from an interference caused by a phase shift the diffracted electron beams, undergo upon propagating across the interface. The phase shift, α, is proportional to the projection of the translation vector, R, onto the diffraction vector, g (i.e. α # g.R). The direction of the translation state can be determined explicitly from the SF contrast in a manner analogous to the analysis of dislocation Burgers vector.An analysis of SF fringes with respect to diffraction theory permits the magnitude of the lattice translation to be evaluated in experimental images.

Geometric nonlinearity (GN) and initial internal forces (IIFs) are the basic characteristics of cable-stayed bridges, but now there is no effective method for analyzing the effect of them on bridge-track interaction of continuous welded rail (CWR) on cable-stayed bridge. A method for reconstructing the displacement-force curve of ballast longitudinal resistance was put forward according to the deformation of cable-stayed bridges under the completed bridge state. A feasibility study on the method was conducted via two aspects of the force and deformation of CWR on a 5 × 40 m single-line simple-supported beam bridge with initial deformation. With the multi-element modeling method and the updated Lagrangian formulation method, a rail-beam-cable-tower 3D calculation model considering the GN and IIFs of cable-stayed bridge was established. Taking a (140 + 462 + 1092 + 462 + 140 m) twin-tower cable-stayed bridge as an example, the impacts of GN and IIFs on bridge-track interaction were comparatively analyzed. The results show that the method put forward to reconstruct ballast longitudinal resistance can prevent the impact of initial deformation of bridge and makes it possible to consider the effect of IIFs of cable-stayed bridge on bridge-track interaction. The GN and IIFs play important roles in the calculation of rail longitudinal force due to vertical bending of bridge deck under train load and the variance of cable force due to negative temperature changes in bridge decks and rails with rail breaking, and the two factors can reduce rail longitudinal force and variance of cable force by 11.8% and 14.6%, respectively. The cable-stayed bridge can be simplified as a continuous beam bridge with different constraints at different locations, when rail longitudinal force due to positive temperature changes in bridge deck and train braking is calculated.

The structure of a prestressed steel structure is complex, which can result in insufficient control accuracy and the low efficiency of the structural safety. The traditional analysis method only obtains the mechanical parameters of the structure and it cannot obtain the key factors that affect the structural safety. In order to improve the intelligence level of the structural safety performance analysis, this study proposes an intelligent analysis for the safety-influencing factors of prestressed steel structures that is based on digital twins (DTs) and random forest (RF). Firstly, the high-precision twin modeling is carried out by the weighted average method. The design parameters and the mechanical parameters of the structure are extracted in real time in the twin model, and the parameters are classified by the RF. The fusion mechanism of the DTs and RF is formed, and the intelligent analysis model of the structural safety factors is established. Driven by the analysis model, the correlation mechanism between the design parameters and the mechanical parameters is formed. The safety state of the structure is judged by the mechanical parameters, and the key design parameters that affect the various mechanical parameters are analyzed. Through the integration of the design parameters and mechanical parameters, the intelligent analysis process of the safety-influencing factors of prestressed steel structures is formed. Finally, an intelligent analysis of the importance of the safety-influencing factors is carried out with the string-supported beam structure as the test object. Driven by the integration of DTs and RF, the key design parameters that affect the various mechanical parameters are accurately obtained, which provides a basis for the intelligent control of the structural safety.

This paper continues the previous study and presents a dynamic modeling approach for a high-speed winding system. To meet the requirements of high-speed winding, a twin-rotor coupling structure is adopted in the winding system. It is a complex spindle system, due to its high speed, heavy load, frequency-dependent coupling parameters, and time-varying rotational speed. In this paper, an approach to establishing a finite element model of the winding system is proposed to predict its dynamic behavior characteristics during the winding process. First, the spindle and contact roller models of the discrete single component are developed based on Timoshenko beam theory. Bending, transverse shear effects, and gyroscopic moment are considered in the models. The contact stiffness between the contact roller and the packages to be wound on the spindle is simplified by a nonlinear spring. The contact stiffness is identified by dynamics analysis in ANSYS® 17.0. Next, a fully dynamic model of the winding system, which consists of the spindle subsystem, the contact roller, and the flexible coupling elements, is established. Third, the Newmark method is used to develop the program to solve the dynamic equations in MATLAB® 2013b. Finally, the effects of the supporting system and contact state on the winding system's dynamic response are investigated. The results indicate the model of the winding system presented in this paper is suitable for predicting dynamic performance during the winding process.

The simultaneous measurement of two Bragg reflections by Bragg coherent X-ray diffraction is demonstrated on a twinned Au crystal, which was prepared by the solid-state dewetting of a 30 nm thin gold film on a sapphire substrate. The crystal was oriented on a goniometer so that two lattice planes fulfill the Bragg condition at the same time. The Au 111 and Au 200 Bragg peaks were measured simultaneously by scanning the energy of the incident X-ray beam and recording the diffraction patterns with two two-dimensional detectors. While the former Bragg reflection is not sensitive to the twin boundary, which is oriented parallel to the crystal–substrate interface, the latter reflection is only sensitive to one part of the crystal. The volume ratio between the two parts of the twinned crystal is about 1:9, which is also confirmed by Laue microdiffraction of the same crystal. The parallel measurement of multiple Bragg reflections is essential for future in situ and operando studies, which are so far limited to either a single Bragg reflection or several in series, to facilitate the precise monitoring of both the strain field and defects during the application of external stimuli.

F357, a hypo-eutectic Al-7%Si-0.6%Mg alloy without beryllium, was processed with CSIR-Rheo technology to the Semi-Solid Metal (SSM) state and cast in plates by means of High Pressure Die Casting. The castings were either left in the as-cast (F) condition or subjected to T4 or T6 heat treatments prior to autogenous Nd:YAG laser welding. A welding operating window was established and within this window, the weld porosity and undercut were minimised. Butt welds complying with ISO 13919-2: 2001 could be produced by means of the optimum parameters of 3.8 kW laser power and a welding speed of 4 m/min with a twin spot laser beam configuration. The mechanical properties of age-hardenable Al-Si-Mg alloys are dependent on the rate at which the alloy is cooled after the solution heat treatment. The low heat input provided by the laser welding process resulted in high enough cooling rates to ensure that both the fusion zone and HAZ were in the T4 condition after welding. Tensile properties equivalent to the parent metal in T6 condition were obtained after subjecting welded T4 plates to conventional artificial ageing treatment.

In the construction process of a prestressed steel structure, it is a point of research interest to obtain the safety state of the structure according to the design parameters and working conditions of the structure. The intelligent prediction of structural construction safety provides the basis for safety control. This study proposes an intelligent prediction method of structural construction safety based on a back propagation (BP) neural network. Firstly, the correlation mechanism of structural construction safety performance parameters is established, which involves structural design parameters and mechanical parameters. According to the basic principle of a BP neural network, the relationship between design parameters and mechanical parameters is captured. The virtual model of a structure construction process is established based on digital twins (DTs). The DTs and BP neural network are combined to form a structural safety intelligent prediction framework and theoretical method, setting working conditions in a twin model to obtain mechanical parameters. Mechanical parameters are intelligently predicted by design parameters in neural networks. The safety performance of structure construction is evaluated according to mechanical parameters. Finally, the intelligent prediction method is applied to the construction process of string beam. Based on DTs and BP neural network, the intelligent analysis of structural construction safety is carried out. This provides a reliable basis for safety control. The feasibility of this research method is verified by comparing the predicted results of the theoretical method with the measured data on site.

We present a conceptual design for a compact X-ray Source BriXS (Bright and compact X-ray Source). BriXS, the first stage of the Marix project, is an Inverse Compton Source (ICS) of X-ray based on superconducting cavities technology for the electron beam with energy recirculation and on a laser system in Fabry-Pérot cavity at a repetition rate of 100 MHz, producing 20–180 keV monochromatic X-Rays devoted mainly to medical applications. An energy recovery scheme based on a modified folded push-pull CW-SC twin Energy Recovery Linac (ERL) ensemble allows us to sustain an MW-class beam power with almost one hundred kW active power dissipation/consumption.

According to earthquake hazard, normal frame structures could hardly avoid failure of ‘Strong Beam and Weak Column’, weak layer and even progressive storey collapse under strong earthquakes, a main reason is the lack of second seismic fortification line in frame structure. Based on the design thought of multiple seismic fortification lines, reinforced concrete twin-frame structure is initiated in this paper. Major feature is increases of redundant constraints and load paths due to added outer limb-columns could take effect as the second seismic fortification line. Twin-frame structure could not only fulfill the demand of ‘three levels, two stages’ in seismic code, but also have been designed through the third stage of ‘resist progressive collapse’, using key member method to promote safety storage and deformability of outer limb-columns, using removal key member method to verify vertical ultimate load of frame beams in weak layer. Though twin-frame structure could not completely avoid plastic hinges in column ends, progressive storey collapse will not appear in this kind of structure. Twin-frame structure is a new structure system which could be applied in constituting new projects as well as strengthening and rebuilding existing projects, further research can be done on this structure system.

An as-cast macrostructure of electron beam additively manufactured metallic materials was represented by coarse columnar grains whose axes were inclined at 25° with respect to the substrate’s plane. One part of the as-grown samples was annealed to form a coarse grain microstructure while the other part was pre-deformed by forging and then annealed what allowed obtaining recrystallized microstructures with small grains and multiple annealing twin boundaries. This sample showed both high strength and plasticity during the tensile tests. These tensile tests demonstrated also two-stage stress-strain curves as depended on their strain hardening rates. High and low strain hardening rates corresponded to a twinning-dominated deformation at stage II and dislocation-base deformation at stage III. A submicron size strain-induced grain-subgrain microstructure was formed in the vicinity of a necked zone as a result of combined twinning/dislocation grain refining.

In order to reduce beam damage, biological TEM specimens are often observed at temperatures close to the boiling point of liquid nitrogen (77 K). Recently, encouraging results on single particles as well as on 2D crystals have appeared, derived from images taken near liquid helium temperature (4 K), in dedicated TEMs. At these temperatures the high resolution frequencies are much better preserved, increasing the allowable dose and thus the signal to noise ratio.4 Here we present the design of a new dedicated Philips He-TEM which combines the full functionality of a CM300 TWIN with a vacuum transfer system and a liquid helium cooled specimen holder.A schematic overview of the Cryo-TEM is shown in figure 1. The key differences compared to a standard CM microscope are: 1) The tip of the specimen rod is cooled below 10 K and the rod itself cannot be taken out of the goniometer (CompuStage). 2) The specimen enters the column on the opposite side.

Current commercial analytical electron microscopes (AEMs) including scanning transmission electron microscopes (STEMs) are a compromise design between the highest spatial, analytical and energy resolutions. in contrast, a VG HB603 STEM at Lehigh University has been designed with a 300 kV cold field-emission gun and twin X-ray detectors to maximize X-ray generation and collection efficiencies [1]. in addition, instrumental features of almost no stray radiation, ultra-high vacuum (<10−7 Pa in the stage and <10−7 Pa in the gun), beam blanking and direct probe-current measurement in the HB 603 have transformed the approaches to quantitative analysis. By using such modern AEMs, it is now possible to perform X-ray microanalysis with the spatial resolution as low as 1.5 nm and the detectability limits of∽2 atoms in the analyzed volume [2]. Furthermore, even quantitative X-ray mapping becomes achievable, while maintaining, high spatial resolution (the original aim of such instruments) [3].

Involvement of the submandibular gland in actinomycotic osteomyelitis in the absence of sinus is rare. Cervicofacial form is characterized by contiguous spread, suppurative osteomyelitic & granulomatous inflammation of the mandible and formation of multiple abscesses and hallmark discharging sinuses draining serosanguinous fluid containing sulphur granules. As the imaging finding of this entity is rarely described, in this case report, a rare case of mandibular actinomycotic osteomyelitis, with a submandibular swelling, but without draining sinus is reported. The imaging findings of cone beam computed tomography (CBCT) & ultrasonography (US) of the case are discussed with a review. In subacute stage, mandibular actinomycosis may show no hallmark sinuses. Sclerotic margins around the lesion may be found on radiograph. Imaging is useful in ruling out clinical diagnostic challenge when it includes involvement of mandible & submandibular region. Cervicofacial actinomycosis commonly occurs as perimandibular infection, rarely as osteomyelitis of the mandible.1 It may present as two distinct morphological patterns; first, "lumpy jaw," and second, simulating an acute pyogenic infection affecting the submandibular area, discharging sinus being a hallmark finding.1 Other variant reported include chronic osteitis, osteolytic lesion, hard nodule on the tongue, lockjaw, periapical, or paradental abscess. Diagnosis of cases presenting in multiple areas in the absence of multiple discharging sinuses is a challenge.2 Usefulness the imaging findings are rarely enumerated. This report is of a twin presentation of a non - sinus forming actinomycotic mandibular osteomyelitis and a submandibular swelling, along with a review of various diagnostic imaging features.

In the article outcomes of probes by definition of influencing the flexibility of pen on optimum requirements of linking of shelves pairwise shrouded blades of turbines are considered. A design feature of such blades is that a composite shank, each half of which has a pen with a bezigless shroud platform, is freely inserted into the groove of disk. The application examples pairwise shrouded blades in turbines of a gas turbine engine (GTD), and also outcomes of the analysis of initial conditions of linking on shroud platforms of such blades are set up. It is shown that under the conditions of operation of the engine, there can be both an interference fit and a clearance on the shroud platform. A description is given of the developed methods for the experimental determination of the initial conditions for pairing the retaining shelves of pairwise shrouded blades and the study of their damping ability and vibration stress. Outcomes of the analysis of requirements of linking of bandage shelves of blading of impellors, experimental researches by definition of their influencing on vibrational stresses and a damping current capacity pairwise shrouded blades and their beam models as systems with a rigorous regular which one is characterized by the elastic-dissipative connection caused both bandages, and tool joints, taking into account flexibility of pen are introduced. It is displayed, that there is the best value of the argument of linking of bandage shelves at which one the maximum damping current capacity of twin blades and according to their minimum of vibrational stresses is reached. Thus, its meaning depends on the flexibility of the pen of a blade. By results of the conducted experimental researches of packages of pairwise shrouded blades of three turbine stages GTD AI-25 and turbine GTD D-36 first stage the relation of the best value of argument Δн, wholesale of linking of bandage shelves from the flexibility of pen which one allows to forecast its value for blades of other stages GTD is constructed. As blades of first stages of turbines GTD AI-322 and D-36 are characterized by flexibility neighbors it is possible to forecast with a high probability, that best values of the argument of linking of their shroud platforms will be one level.

We measure the population distribution in one of the atomic twin beams generated by four-wave mixing in an optical lattice. Although the produced two-mode squeezed vacuum state is pure, each individual mode is described as a statistical mixture. We confirm the prediction that the particle number follows an exponential distribution when only one spatio-temporal mode is selected. We also show that this distribution accounts well for the contrast of an atomic Hong–Ou–Mandel experiment. These experiments constitute an important validation of our twin beam source in view of a future test of a Bell inequality.

Twin screw pumps are positive displacement machines. Two meshing screws connected by timing gears push the fluid trapped in the screw cavities axially from suction to discharge. Available steady state hydraulic models predict pump performance and axial pressure distribution in the chambers in single- and two-phase flow conditions. However, no model is available for their rotordynamics behavior. Due to the helix angle of the screw, the pressure distribution around the rotor is not balanced, giving rise to both static and dynamic lateral forces. The work presented here introduces a starting point for rotordynamic analysis of twin screw pumps. First, we show that the screw rotor's geometry can be represented by axisymmetric beam elements. Second, we extend the steady state hydraulic model to predict both the static and dynamic lateral forces resulting from the unbalanced pressure field. Finally, hydraulic forces are applied to the rotor to predict static, synchronous, and nonsynchronous responses. Predictions of the dynamic pressure were compared to measurements from the literature and were found to be in good agreement.

AbstractA compact annealing machine with all solid-state green lasers has been developed, which has the advantage of widely adjustable solidification rate through the delay time control of two long pulses (pulse width ~100ns). Advanced lateral crystal growth (ALCG) process has been proved by the double-pulsed all solid-state laser annealing. The laser beam has a line shape 0.1mm wide and 17mm long, and the beam profile on the short axis is quasi-Gaussian (FWHM 0.1mm). Scanning the line beam along the short axis at the 86% overlapping ratio, the lateral crystal growth area of width 14μm, parallel to the long axis, is sequentially formed at the pitch of 14μm towards the scanning direction. The advanced lateral growth mechanism is easily explained as follows: (1) At the first irradiation, twin seed lines of width 4μm, parallel to the long axis, generates at a boundary between a near-complete melting region and a complete melting region. (2) At the second irradiation of scanning step 14μm, the front seed line in the scanning direction grows symmetrically toward both sides. (3) At the third irradiation of scanning step 2x14μm, the seeds laterally grow until stopped by the growing of seeds on both sides. Finally the ALCG process by the scanning line-beam technique like the current ELA enables us to produce the laterally grown Si thin-films sequentially arranging the belt-shaped texture at the pitch of 14μm. The quality of the laterally grown Si films is quite well except for the projections generated by the bump of lateral growing seeds.

ABSTRACTChanges induced by 1.5 MeV Kr ion irradiation of both U3Si and U3Si2 have been followed by in situ transmission electron microcopy. When irradiated at sufficiently low temperatures, both alloys transform from the crystalline to the amorphous state. When irradiated at temperatures above the temperature limit for ion-beam amorphization, both compounds disorder, with the Martensite twin structure in U3Si disappearing from view in TEM. Prolonged irradiation of the disordered crystalline phases results in nucleation of small crystallites within the initially large crystal grains. The new crystallites increase in number during continued irradiation until a fine grain structure is formed. Electron diffraction yields a powder-like diffraction pattern that indicates a random alignment of the small crystallites. During a second irradiation at lower temperatures, the small crystallizes retard amorphization. After 2 dpa at high temperatures, the amorphization dose is increased by over twenty times compared to that of initially unirradiated material.

Abstract The design and demonstration of a new version of the force measurement system based on the resonance principle by involving shape memory alloy (SMA) is presented. The sensor design enables an electromechanically functional resonator comprising the cantilever beam as the vibratory structural element and the Joule heated SMA as an actuating element. The actuation frequency of the SMA wire is improved up to 5.5 Hz by the optimized activation parameters and an appropriate biasing element. The choice of design attributes of the sensing module is made based on the analysis of the associated technical parameters with different dimensions of the constituents of the sensing assembly. The sensing module that adopts the least stiff configuration by the series arrangement of the active SMA and passive elastic cantilever element is modeled mathematically. The dual/twin phenomena of the SMA wire featured by both, actuation that creates resonance in the structure and self-sensing that senses the resonance state, is deployed. The sensor possesses static sensing capabilities and detects force in the range of 0.785 N to 2.45 N and this scheme of force measurement could be a stand-alone unit, besides is adaptable as an application-specific sensor in the analysis of large flexible structures.

The theory, design, and use of a focusing laser differential interferometer (FLDI) instrument are described. The FLDI is a relatively simple, nonimaging, common-path polarization interferometer for measuring refractive signals generated by turbulence, as well as small-amplitude acoustics and boundary-layer instabilities. It has in principle a unique ability to look through wind-tunnel windows, ignore sidewall boundary-layers and vibration, and concentrate only on the refractive signal near a pair of sharp beam foci in the core flow. The instrument's low cost and ease of implementation make it a promising alternative to traditional hot-wire anemometry (HWA) and particle-based methods for turbulence characterization. A matrix equation is written for the overall optical behavior of the FLDI, and transfer functions are developed to account for spatial filtering, f/number of the field lenses, various turbulence profiles, etc. Benchtop experiments using a turbulent sonic airjet demonstrate the focusing ability of the FLDI, its frequency response, and unwanted signal rejection. The instrument is also used to optically interrogate the flow in the Penn State Supersonic Wind Tunnel and in USAF AEDC Hypervelocity Tunnel 9, where it made preliminary measurements of freestream disturbance levels and power spectra. A central feature of the FLDI used here is the replacement of traditional fixed Wollaston birefringent prisms with variable Sanderson prisms for separation and recombination of the helium–neon laser beams, and for the accurate setting of micrometer-range beam separation distances required for successful turbulence measurements. The instrument also features phase compensation of the output, where perpendicularly polarized light signals are separately sensed by the twin photodetectors. This provides a unique ability to measure the coherence of turbulent spectra and thus to reject low-coherence noise.

Abstract Two time-reversal quantum key distribution (QKD) schemes are the quantum entanglement based device-independent (DI)-QKD and measurement-device-independent (MDI)-QKD. The recently proposed twin field (TF)-QKD, also known as phase-matching (PM)-QKD, has improved the key rate bound from O(η) to O$$(\sqrt{{\boldsymbol{\eta }}})$$ ( η ) with η the channel transmittance. In fact, TF-QKD is a kind of MDI-QKD but based on single-photon detection. In this paper, we propose a different PM-QKD based on single-photon entanglement, referred to as single-photon entanglement-based phase-matching (SEPM)-QKD, which can be viewed as a time-reversed version of the TF-QKD. Detection loopholes of the standard Bell test, which often occur in DI-QKD over long transmission distances, are not present in this protocol because the measurement settings and key information are the same quantity which is encoded in the local weak coherent state. We give a security proof of SEPM-QKD and demonstrate in theory that it is secure against all collective attacks and beam-splitting attacks. The simulation results show that the key rate enjoys a bound of O$$(\sqrt{{\boldsymbol{\eta }}})$$ ( η ) with respect to the transmittance. SEPM-QKD not only helps us understand TF-QKD more deeply, but also hints at a feasible approach to eliminate detection loopholes in DI-QKD for long-distance communications.

In some ancient Greek drama plays, the stage machine used to bring the gods or the heroes of the tragedy on stage, known with the Latin term deus-ex-machina, was used for the solution of an apparently insoluble crisis. A twin-facing stone base was found in the theater of Phlius in Corinthia, Greece, behind the stage building. The existence of similar foundations in other ancient theaters indicates their use for specific purposes connected with the needs of the play. An attempt to reconstruct the mechanism is presented based on archeological evidence and literary descriptions. The reconstructed mechanism was designed for path generation and comprised a single beam with ropes controlling its planar motion and a sidle twin lifting system.

AbstractMicrostructural changes in a Ba2YCu3O7 pellet were continuously observed during electron irradiation in a transmission electron microscope operating at 200 kV. Twin lamellae of 2~10 nm in thickness with 1~50 nm spacings were seen parallel to the lattice image of (001) plane with 1.17 nm in lattice spacing. The tip of the twin was lenticular and the (001) lattice fringes were distorted around the tip. Upon intense electron beam illumination, the lamellae faded at the tip and the thickness gradually decreased which increased the spacing in the high density region. Defect clusters of about 10 nm in size were produced in the very early stage of electron illumination.

In The Practice of Everyday Life, Walking in the City, Michel de Certeau celebrates the glorious sublimity of an Icarian moment as his gaze from the 110th floor of the World Trade Centre soars over Manhattan. Having taken such a voluptuous pleasure (92) in the view myself, and watched the twin towers collapse into rubble on my television screen last September, as I re-visit the aerial site through de Certeau, his words resonate strongly with the oneiric force of memory, myth and the wonder of urban possibility. For while theorising, does de Certeau not write his own story of the city as dream, as imaginative longing, consuming and producing an urban 'text' (93) as he reads from on high? Participating in the logic of one of the city's opportunities, a tourist attraction, his analytic practice is a creative expression of his own subjective experience. Theoretically, the story begins in the labyrinth of the cityscape, where the urban text is humanised by its mobile, unpredictable practitioners whose everyday operations style, invent and generate ways of being and becoming. What de Certeau offers us is something quite beautiful and noble, almost consolatory, in the idea of an artful, other spatiality that slips, undetected, into the banal routine of daily existence. To explore how lived space (96) is authorised by its heroic practitioners, made other, as it is inscribed into and outside the historic, social and economic realities or strategies of the urban environment, I resort to fiction, where the certain strangeness (93) of the everyday surfaces to be read. Colum McCann's novel, This Side of Brightness, takes us down below de Certeau's down below to the subterranean spaces of the New York City subway tunnels where the central character, Treefrog, estranged from his family, makes his home: his dark nest, high in the tunnel (McCann 2). Treefrog's escape into this murky, cavernous netherworld is a disappearing act for this is where no ordinary practitioners of the city live 'down below,' [down] below the thresholds at which [an everyday] visibility begins. (de Certeau 93) Seeking refuge, this is where the city's resident asylum seekers migrate, claiming exile as a right. To be outcast is an autonomous and pragmatic spatial tactic, a self-imposed, self-composed state of being as other. Here, survival is a process of resistance, an illegal occupation. Errant and devious, the lifestyle choice these urban consumers make violates the civil ordinances of the city. Venturing topside, Treefrog repels, offends and embarrasses the ordinary practitioners of the city travelling on the subway (96, 240) and in the reading room at the public library (93). The disgust and fear aroused by his stench and squalid appearance make no allowance for pity or pride. In these aboveground collective social spaces his unhygienic, undomesticated presence is not proper; it signals defiance in its fetid, imposing refusal to be controlled or to disappear. Treefrog is an anonymous manifestation of the cityscape. Disguised by long hair, a beard, ragged clothes, filth and dirt (242), his real identity is undetectable: Clarence Nathan Walker is invisible. Seemingly primitive, this sight is decidedly modern in its ubiquitous depiction of the contemporary urban indigent. A place of wounded spirits, Treefrog's 'mole' neighbourhood confesses the shame of an overwhelming suffering born of the streets. Papa Love's grief is monumentalised in the surreal gargantuan murals and portraits of the dead he paints on the walls of the tunnel. Crack addicts, Angela and Elijah, get high, wasted, underground. A symbolic toilet seat hangs wreath-like on Faraday's front door; as a doorbell (128). Dean, the Trash Man, collects the discarded remains of an urban consumer society and installs them in his 'front yard' as an assemblage of ready-made materials and found objects. Textually, his 'work' orchestrates a cacophony of human ruin and putrescence: the mounds of human faeces and the torn magazines and the empty containers and the hypodermic needles with blobs of blood at their tips like poppies erupting in a field...the broken bottles and rat droppings and a baby carriage and smashed TV and squashed cans and discarded cardboard boxes and shattered jars and orange peels and crack vials and a single teddy bear with both its eyes missing, its belly nibbled into by rats. (56) In this community, housing isolates, shelters and incarcerates, each inhabitant has their own cubicle, concrete bunker, solitary cell (56). In contrast to this depressed existential vista, before his incarnation as Treefrog, Clarence Nathan knows the sublime erotic charge of towering over New York City, expressed by de Certeau. Working construction on the city's skyscrapers, he seeks ascension, going, willfully, higher than any walking man in Manhattan....Beneath him, Manhattan becomes a blur of moving yellow taxis and dark silhouettes. There is something in this rising akin to desire, the gentle rock from side to side, the cooling breeze, the knowledge that he is the one who will pierce the virginity of space where the steel hits the sky....The elevator clangs and stops. Clarence Nathan finishes his coffee, tosses the paper cup and walks across the metal decking towards two ladders which jut up in the air. For a joke the men call this area the POST: The Place of Shrivelled Testicles. No ordinary man will go further. The nimblest Clarence Nathan and Cricket...climb three ladders to the very top of the building, where columns of steel reach up into the air. (195-6) Unaffected by vertigo and impervious to the danger, there is a seeming nonchalance, a banality, to Clarence Nathan's activity as he finishes his coffee, tosses the paper cup and gets to work; this is a practice of everyday life for him. And yet this productive activity, governed by city council planning and approval, contains a liberatory ruse, an 'anthropological,' poetic and mythic experience of space, (93) as proposed by de Certeau. High above, he performs a transcendent manoeuvre, a magic trick, creating and constructing space out of thin air, nothing. Icarian, Clarence Nathan's desire seems not for scopic pleasure but for the pure visceral elation of being unrestrained, unprotected, autonomous, above and beyond the rest of the world. At such a height Clarence Nathan does not speculate or even think he forgets where he is, that his 'body even exists.' (177) Surpassing rational comprehension and linguistic expression, his elevation articulates an unadulterated liberation, an erotics of feeling and an ecstasy of being: [s]ometimes, for a joke, Clarence Nathan takes out his harmonica at the top of the column and blows into it using just one hand. The wind carries most of the tune away, but occasionally the notes filter down to the ironworkers below. The notes sound billowy and strained, and for this the men sometimes call him Treefrog, a name he doesn't much care for. (198) From this pivotal point, high on the extreme vertical axis of the cityscape, Clarence Nathan has much further to fall when he loses his balance mentally, descending into an abyss of human despair. Being down is not deep enough. Going underground, Clarence Nathan reclaims this haunted, burrowed space of the city as a legacy bequeathed to him by his grandfather, one of the sandhogs who dug the tunnels of the New York subway, and reinvents himself as Treefrog. An appropriate moniker for this uncivilised, otherworldly realm, [a]ll darkness and dampness and danger, (7) sometimes it is the only name he can remember (29). Foregrounding memory and myth, McCann's fable weaves the creation story of a family through the interstices of a city's legends and official history, allowing us to read the appropriation, the othering, of the city's spaces by its inhabitants in the practice of their lives as ephemeral markings of artistic activity. Through the incantation of spatial and narrative trajectories, as de Certeau suggests, [a] migrational, or metaphorical, city thus slips into the clear text of the planned and readable city (93). Writing himself into these catacombs, literally, Treefrog embraces his interment, his burial rights, as a return to his primordial home: In his notebook Treefrog writes: Back down under the earth, where you belong. Back down under the earth where you belong....He could make a map of those words, beginning at the B and ending at the g where all beginning begins and ends and they would make the strangest of upground and belowground topographies. (139) So as not to forget the strange topographies of existence, Treefrog inscribes them on the surface of his skin: [h]is chest is scrimshawed with stabwounds and burns and scars. So many mutilations of his body. Hot paper clips, blunt scissors, pliers, cigarettes, matches, blades they have all left their marks. (30) Mapping an abstract expression, intimately, these are the warrior scars of the initiate. Belowground, Clarence Nathan eludes the clinical strategies of his obsessive-compulsive post-traumatic stress disorder; he avoids the nuthouse (228). Here, in retreat, as Treefrog, he is free to create, dream and imagine, unrestrained and unexamined; it is an elegant self-prescribed remedy. For Clarence Nathan, the tunnels are therapeutic and restorative. Ultimately, they enable him to be resurrected back into the light, upground, leaving Treefrog, like a discarded doppelgänger, to the shadows of the tunnels (242-3). An ironic compensation for his mental instability, Clarence Nathan's gift of perfect physical balance, his inheritance, (170) determines his survival underground. Safe and secure with his cave positioned high in the tunnel wall, Treefrog's daily movements are dependent upon the demonstration of an agile bodily grace, a mobility that defies gravity in its series of acrobatic swings and precarious tight-rope walking. Enhancing the danger and difficulty of his daring by performing blindfolded, Treefrog negotiates space intuitively: he walks onto the catwalk with his eyelids shut. The narrow beam requires supreme balance below him is a twenty foot drop to the tunnel. He swings his way down to the second beam ten feet below, crouches, then leaps and drops soundlessly to the gravel, knees bent, heart thumping. He opens his eyes to the darkness. (25) Mimetically Treefrog appropriates this eternal nocturnal realm and makes it his own, a part of himself, he feels the darkness, smells it, belongs to it. (23) As from his subterranean perch Treefrog fills the emptiness with the eerie, improvised strains of his harmonica, the stale, dank, tired air of the tunnels, is filtered through the human body, and used to make something strangely ethereal, beautiful, fresh and new: in the miasmic dark, Treefrog played, transforming the air, giving back to the tunnels their original music (2). Treefrog accepts this other spatiality, carved into and out of the urban environment, as a gift, and his performance reciprocates a generosity that signals hope and healing; '[t]he world, he knows, can still spring its small and wondrous surprises (53). McCann presents the tunnels of New York City as an urban wilderness, a lawless frontier. And yes, Treefrog's community is comprised of "demonic subterraneans madmen, perverts, addicts, criminals, murderers," but challenging Blanche Gelfant's account of the lower states, this reverse spatial direction does not necessarily signify a metaphorical mobilisation of values downward into the unexplored depths of moral disorder (417). Rather, in This Side of Brightness, moral disorder is a condition of ordinary, everyday existence aboveground, where violence, chaos, vulnerability, persecution, terror, inequality, kindness, disregard, compassion, indifference, awe, tragedy, compose, socially, [a] landscape of loving and hating. A palpable viciousness in the air. And yet a tenderness too. Something about this part of the world being so alive that its own heart could burst from the accumulated grief. As if it all might suddenly fulminate under the gravity of living. (185) Figured imaginatively through Treefrog the tunnels become an enchanted otherworldly space, '[a] heaven of hell,' (70) in which darkness, solitude and anonymity have the miraculous power to strengthen and absolve. Amidst the waste and detritus a beauty is brutally, painfully laid bare. For Treefrog, for Clarence Nathan, the tunnels are an emotional and psychological sanctuary and their appropriation is a courageous life-affirming act: it is only underground that...men become men, integrated, whole (37). References de Certeau, Michel. The Practice of Everyday Life. Trans. Steven Rendall. Berkeley: U of California P, 1988. Gelfant, Blanche. Residence Underground: Recent Fictions of the Subterranean City. The Sewanee Review. 83 (1975): 406-38. McCann, Colum. This Side of Brightness. London: Phoenix House, 1998. Citation reference for this article MLA Style Williams, Marisa. "Going Underground" M/C: A Journal of Media and Culture 5.2 (2002). [your date of access] < http://www.media-culture.org.au/0205/underground.php>. Chicago Style Williams, Marisa, "Going Underground" M/C: A Journal of Media and Culture 5, no. 2 (2002), < http://www.media-culture.org.au/0205/underground.php> ([your date of access]). APA Style Williams, Marisa. (2002) Going Underground. M/C: A Journal of Media and Culture 5(2). < http://www.media-culture.org.au/0205/underground.php> ([your date of access]).