Literatura académica sobre el tema "Postcompression"

Elastography is based on the estimation of strain due to tissue compression or expansion. Conventional elastography involves computing strain as the gradient of the displacement (time-delay) estimates between gated pre- and postcompression signals. Uniform temporal stretching of the postcompression signals has been used to reduce the echo-signal decorrelation noise. However, a uniform stretch of the entire postcompression signal is not optimal in the presence of strain contrast in the tissue and could result in loss of contrast in the elastogram. This has prompted the use of local adaptive stretching techniques. Several adaptive strain estimation techniques using wavelets, local stretching and iterative strain estimation have been proposed. Yet, a quantitative analysis of the improvement in quality of the strain estimates over conventional strain estimation techniques has not been reported. We propose a two-stage adaptive strain estimation technique and perform a quantitative comparison with the conventional strain estimation techniques in elastography. In this technique, initial displacement and strain estimates using global stretching are computed, filtered and then used to locally shift and stretch the postcompression signal. This is followed by a correlation of the shifted and stretched postcompression signal with the precompression signal to estimate the local displacements and hence the local strains. As proof of principle, this adaptive stretching technique was tested using simulated and experimental data.

Summary. In the postcompression period of crush syndrome regenerative processes develop restorative processes in target organs, in particular in the heart. However, the dynamics of myocardial regenerative changes in the postcompression period in crush syndrome is insufficiently covered in professional literature and requires comprehension study and clarified. The aim of the study – to find out features of regenerative changes in heart of laboratory rats in the dynamics in the postcompression period of crush syndrome. Materials and Methods. Light-optical and polarization were performed examination of the myocardium of 48 laboratory rats after 1, 3, 7 and 14 days (12 animals in each period) after cessation of 6 hour compression of the thigh right pelvic limb. Crush syndrome was modeled under anesthesia by intraperitoneal input of ketamine hydrochloride (100 mg/kg body weight) in a specially designed device, the compression force was 7 kg/cm2, the compressive surface area – 5 cm2. The control group consisted of 12 animals. Results. The stages of myocardial remodeling in the postcompression period are noted, reflecting its structural recovery. In the early postcompression period light-optical disorders predominated microcirculation and alternate changes in acquired cardiomyocytes maximum development after 3 days. After 7 days in myocardial stroma registered cellular infiltrates in which predominate lymphocytes and fybroblasts. Cardiomyocytes lose a compact, gait cells became fortuous, microfoci of contractures were detected and fragmentation, there was a weak proliferation of collagen fibers. After 14 days in the late postcompression period the manifestation do not fade microcirculation disorders. Processes were registered in some areas collagen formation. Conclusions. In the first three days after the cessation of compression of compression of the lower extremity dystrophic–necrotic changes of the myocardium persist in combination with microcirculatory disorders. After 7 days the development of interstitial lympho–histiocytic infiltration is observed against the background of a gradual decrease alternative and hemodynamic processes. After 14 days registration a restoration of myocardial histostructure with residual processes of microfocal contracture of cardiomyocyte degeneration and increased collagen formation are registere

Objective: Crush syndrome (CS) remains a life-threatening condition. This research aims to investigate the changes of the macro- and microelement content in blood, liver and bone tissue in a rat model of CS. Methods Studies were conducted on 40 nonlinear mature white male rats. The left hind limb of the rat was subjected to the mechanical pressure for 4 hours. The compressed area was 4 cm with a compressive 2 2 force of 4.25 kg/cm . Determination of total calcium, magnesium and inorganic phosphate contents in blood serum was performed on a semi-automatic biochemical analyser Humalyzer 2000 (Human, Germany) using standard reagent kits. The content of calcium, magnesium, copper and zinc in the liver and bone tissue was determined by atomic absorption spectrometry on a Selmi C-115 M spectrophotometer. Results: It was found that serum content of calcium decreased on the 1st day of observation (by 10.1%), but increased on the 14th day (by 23.0%); the magnesium content progressively decreased during postcompression period, and the content of inorganic phosphate increased on the 14th day of observation by 36.6% (p<0.05) exeeded control data. The content of calcium in the liver tissue started to increase on the 3rd day of observation, and on 14th day by 25.9% (p<0.05) exceeded the control data. Magnesium content in the liver tissue was progressively decreasing during all days of observation. At the same time the content of zinc and copper in the liver tissue gradually increased during postcompression period. The content of calcium, magnesium, zinc and copper in the bone tissue significantly changed from the 3rd day of the postcompression period, in particular the content of bioelements vs. control group progressively decreased by 30.6%, 42.7%, 43.9% and 30.1% respectively on the 14th day of observation. Conclusion : The postcompression period in a rat model of CS is characterized by the pronounced imbalance of macro- and microelements content in blood, liver and bone tissues, which is important for the regulation of metabolic processes. These findings warrant further studies and can be used for developing new treatments that are efficient for dysmacro- and dysmicroelementosis that develop in case of experimental CS. Bangladesh Journal of Medical Science Vol. 23 No. 03 July’24 Page : 714-721

Ondansetron tablets that are directly compressed using crospovidone and croscarmellose as a synthetic super disintegrant are the subject of this investigation. A central composite, response surface, randomly quadratic, nonblock (version 13.0.9.0) 32 factorial design is used to optimize the formulation (two-factor three-level). To make things even more complicated, nine different formulation batches (designated as F1–F9) were created. There were three levels of crospovidone and croscarmellose (+1, 0, -1). In addition to that, pre- and postcompressional parameters were evaluated, and all evaluated parameters were found to be within acceptable range. Among all postcompressional parameter dispersion and disintegration time, in vitro drug release experiments (to quantify the amount of medication released from the tablet) and their percentage prediction error were shown to have a significant influence on three dependent variables. Various pre- and postcompression characteristics of each active component were tested in vitro. Bulk density, tap density, angle of repose, Carr’s index, and the Hausner ratio were all included in this analysis, as were many others. This tablet’s hardness and friability were also assessed along with its dimension and weight variations. Additional stability studies may be conducted using the best batch of the product. For this study, we utilised the Design-Expert software to select the formulation F6, which had dispersion times of 17.67 ± 0.03 seconds, disintegration times of 120.12 ± 0.55 seconds, and percentage drug release measurements of 99.25 ± 0.36 within 30 minutes. Predicted values and experimental data had a strong correlation. Fast dissolving pills of ondansetron hydrochloride may be created by compressing the tablets directly.

The current research work involves preparation of fast dissolving tablets of Aceclofenac by direct compression method using different concentrations of Lepidium sativum mucilage as natural superdisintegrant. A two-factor three-level (32) factorial design is being used to optimize the formulation. Nine formulation batches (D1–D9) were prepared accordingly. Two factors as independent variables (X1-amount of β-cyclodextrin and X2-amount of Lepidium sativum mucilage) were taken with three levels (+1,0,-1). The levels of two factors were selected on the basis of preliminary experiments conducted and their effect on three dependent variables (disintegration time, wetting time, and in vitro drug release) was studied along with their % prediction error. All the active blends were evaluated for postcompression parameters (angle of repose, Carr’s index, Hausner ratio, etc.) and the tablets were evaluated for postcompression parameters (weight variation, hardness, and friability, wetting time, disintegration time, water absorption ratio, and in vitro drug release studies). The optimum batch was further used for SEM and stability studies. Formulation D5 was selected by the Design-Expert software which exhibited DT (15.5 sec), WT (18.94 sec), and in vitro drug release (100%) within 15 minutes.

La génération d'harmoniques d'ordres élevés est un phénomène physique non linéaire qui se produit en focalisant une impulsion de durée femtoseconde (1 fs = 10⁻¹⁵ s) dans un gaz rare. Elle permet de produire des spectres dans le domaine UV/XUV, se présentant sous forme d'un peigne de fréquences. L'intérêt croissant pour la génération d'harmoniques d'ordres élevés vient du fait que les spectres XUV générés sont compatibles, dans le domaine temporel, avec la production d'impulsions attosecondes (1 as = 10⁻¹⁸ s). Ces impulsions sont d'un grand intérêt dans l'étude de dynamiques électroniques complexes, de temps de photoémissions dans des atomes ou molécules, ou encore dans des applications industrielles telles que l'étude de la lithographie. Les dynamiques au cœur des atomes se déroulent sur des échelles de l'unité atomique de temps, avec une unité atomique de temps équivalant à 24 as. La production de ces impulsions attosecondes est donc pertinente pour étudier ces phénomènes au cœur même des atomes. Plus particulièrement, nous nous intéressons ici à la génération de trains d'impulsions attosecondes courts et d'impulsions attosecondes isolées. La génération d'harmoniques d'ordres élevés permet d'obtenir des trains d'impulsions attosecondes, et nous cherchons à isoler une impulsion dans le train d'impulsions. Cela se traduit spectralement par la recherche d'un spectre XUV continu. Dans cette thèse, nous nous intéressons à la génération de ces spectres XUV continus, ainsi qu'à la caractérisation temporelle des impulsions femtosecondes et attosecondes. Le point d'action se trouve dans le confinement temporel de l'émission XUV. Dans une première partie, nous montrons une méthode robuste afin de diminuer la durée des impulsions fondamentales jusqu'à une durée de quelques cycles optiques. Cette mise en forme spectrale amène plusieurs applications subsidiaires pour la mise en forme spectrale du spectre harmonique. Dans une seconde partie, nous présentons une deuxième méthode pour confiner l'émission XUV, en modulant temporellement la polarisation de l'impulsion fondamentale, avec la méthode dite de "porte de polarisation". De nouvelles configurations de la porte de polarisation et les effets spectraux associés au confinement temporel y sont décrits. Dans une troisième partie, nous présentons la combinaison des deux méthodes évoquées dans les deux premières parties, afin d'obtenir des spectres XUV continus compatibles avec la génération d'impulsions attosecondes isolées. Ces spectres continus ont été obtenus dans deux laboratoires, avec deux systèmes expérimentaux différents. Dans une dernière partie, nous nous intéressons à la caractérisation des impulsions XUV femtosecondes et attosecondes. En particulier, nous présentons une caractérisation classique basée sur un signal de photoélectrons, permettant de caractériser des impulsions de quelques centaines d'attosecondes, jusqu'à une impulsion attoseconde isolée. Nous proposons également deux nouvelles méthodes, basées sur l'observation du signal de photons XUV et sur la modulation de polarisation de l'impulsion fondamentale. Par ces méthodes, nous cherchons à reconstruire les enveloppes temporelles des harmoniques
High order harmonic generation is a nonlinear physical phenomenon that occurs by focusing a femtosecond-duration pulse (1 fs = 10^-15 s) in a rare gas. It allows the production of spectra in the UV/XUV range, appearing as a frequency comb. The growing interest in high-order harmonic generation stems from the fact that the generated XUV spectra are compatible, in the time domain, with the production of attosecond pulses (1 as = 10^-18 s). These pulses are of great interest in the study of complex electronic dynamics, photoemission times in atoms or molecules, or even in industrial applications such as lithography studies. Dynamics at the core of atoms occur on atomic time unit scales, with one atomic unit of time equivalent to 24 as. The production of these attosecond pulses is thus relevant for studying these phenomena at the very core of atoms. More specifically, we are interested here in the generation of short attosecond pulse trains and isolated attosecond pulses. High-order harmonic generation allows obtaining attosecond pulse trains, and we seek to isolate one pulse within the pulse train. Spectrally, this translates to the search for a continuous XUV spectrum. In this thesis, we focus on generating these continuous XUV spectra, as well as on the temporal characterization of femtosecond and attosecond pulses. The key aspect lies in the temporal confinement of the XUV emission. In the first part, we demonstrate a robust method to reduce the duration of the fundamental pulses to a few optical cycles. This spectral shaping leads to several subsidiary applications for the spectral shaping of the harmonic spectrum. In the second part, we present a second method to confine the XUV emission by modulating the polarization of the fundamental pulse temporally, using the so-called "polarization gating" method. New configurations of the polarization gate and the spectral effects associated with temporal confinement are described. In the third part, we present the combination of the two methods mentioned in the first two parts to obtain continuous XUV spectra compatible with the generation of isolated attosecond pulses. These continuous spectra were obtained in two laboratories with two different experimental systems. In the final part, we focus on the characterization of femtosecond and attosecond XUV pulses. In particular, we present a classical characterization based on photoelectron signal, allowing the characterization of pulses whose durations are few hundred attoseconds, up to an isolated attosecond pulse. We also propose two new methods based on the observation of the XUV photon signal and the modulation of the polarization of the fundamental pulse. Through these methods, we seek to reconstruct the temporal envelopes of the harmonics

By cascaded focusing and compressing, we demonstrated 50-fold postcompression of carrier-envelope-phase-stabilized, 157 fs and 1.34 mJ pulses at 1030 nm down to 3.1 fs (single-cycle) with a pulse energy of 0.98 mJ.

We introduce the bow tie multi-pass cell as a new scheme for post-compression of high-energy laser pulses, overcoming current limits of Herriott-type multi-pass cell-based postcompression imposed mainly by mirror damage threshold limitations.