Search results for "frequency"
showing 10 items of 2158 documents
Effect of physical aging on the low-frequency vibrational density of states of a glassy polymer
2003
The effects of the physical aging on the vibrational density of states (VDOS) of a polymeric glass is studied. The VDOS of a poly(methyl methacrylate) glass at low-energy (<15 meV), was determined from inelastic neutron scattering at low-temperature for two different physical thermodynamical states. One sample was annealed during a long time at temperature lower than Tg, and another was quenched from a temperature higher than Tg. It was found that the VDOS around the boson peak, relatively to the one at higher energy, decreases with the annealing at lower temperature than Tg, i.e., with the physical aging.
Double-quantum nutations in a two-level spin system
1986
The transient oscillatory behavior of the nonlinear response of a two-level electron-spin system is experimentally investigated in a sample of glassy silica with ${E}_{1}^{\mathcal{'}}$ centers (S=(1/2)) at microwave frequency at T=4.2 K. The transient regime, excited by an intense step-modulated radiation tuned to double-quantum (DQ) resonance, is monitored by revealing the second-harmonic (SH) wave radiated by the spins undergoing DQ transitions. Time- and frequency-domain results show that the emitted SH wave has two components: the former, which vanishes at the DQ resonance, exhibits an overdamped transient regime, the latter consists of damped oscillations at a frequency which depends …
Eye Cataract Simulation Using Polymer Dispersed Liquid Crystal Scattering Obstacles
2004
Polymer dispersed liquid crystals with electrically induced variations of light scattering extent similar to that of transparent PLZT ceramics are used for simulation of different development stages of eye cataract. Wavelength dependencies of scattering are determined in the visible spectral range, and human visual response looking through the scattering obstacle to the onset of various spatial frequency stimuli is determined psychophysically and electrophysiologically in order to find correlation between the scattering extent, visual acuity and visual evoked potential VEP chromatic characteristics.
Genome-wide detection of copy-number variations in local cattle breeds
2019
The aim of the present study was to identify copy-number variations (CNVs) in Cinisara (CIN) and Modicana (MOD) cattle breeds on the basis of signal intensity (logR ratio) and B allele frequency of each marker, using Illumina’s BovineSNP50K Genotyping BeadChip. The CNVs were detected with the PennCNV and SVS 8.7.0 software and were aggregated into CNV regions (CNVRs). PennCNV identified 487 CNVs in CIN that aggregated into 86 CNVRs, and 424 CNVs in MOD that aggregated into 81 CNVRs. SVS identified a total of 207 CNVs in CIN that aggregated into 39 CNVRs, and 181 CNVs in MOD that aggregated into 41 CNVRs. The CNVRs identified with the two softwares contained 29 common CNVRs in CIN and 17 co…
High-contrast sub-Doppler absorption spikes in a hot atomic vapor cell exposed to a dual-frequency laser field
2017
International audience; The saturated absorption technique is an elegant method widely used in atomic and molecular physics for high-resolution spectroscopy, laser frequency standards and metrology purposes. We have recently discovered that a saturated absorption scheme with a dual-frequency laser can lead to a significant sign reversal of the usual Doppler-free dip, yielding a deep enhanced-absorption spike. In this paper, we report detailed experimental investigations of this phenomenon, together with a full in-depth theoretical description. It is shown that several physical effects can support or oppose the formation of the high-contrast central spike in the absorption profile. The physi…
Vārdu savienojumu variācijas angļu valodas variantu tīmekļa korpusos
2020
Kopš pasaulē internets ir kļuvis aizvien pieejamāks, palielinājusies arī saziņa starp cilvēkiem visā pasaulē. Šāda informācijas apmaiņa var izraisīt globalizācijas efektu valodās vai valodu variantos, it īpaši valstiskajā līmenī. Neraugoties uz to, dažādi pētnieki ir analizējuši dažādās pasaules valstīs lietotās angļu valodas variāciju atšķirības, nevis līdzības. Tādējādi šā, uz korpusu balstītā pētījuma mērķis ir analizēt kolokācijas, pamatojoties uz izvēlēto lietvārdu sarakstu, kas veidots, izmantojot četras nacionālās angļu valodas variantus – amerikāņu, austrāliešu, britu un kanādiešu. Analīze tika veikta divos korpusos – Corpus of Global Web-Based English (GloWbE) un Corpus of Four Nat…
Shift-Invariant Canonical Polyadic Decomposition of Complex-Valued Multi-Subject fMRI Data with a Phase Sparsity Constraint
2020
Canonical polyadic decomposition (CPD) of multi-subject complex-valued fMRI data can be used to provide spatially and temporally shared components among groups with both magnitude and phase information. However, the CPD model is not well formulated due to the large subject variability in the spatial and temporal modalities, as well as the high noise level in complex-valued fMRI data. Considering that the shift-invariant CPD can model temporal variability across subjects, we propose to further impose a phase sparsity constraint on the shared spatial maps to denoise the complex-valued components and to model the inter-subject spatial variability as well. More precisely, subject-specific time …
Evaluation of the primary stability in dental implants placed in low density bone with a new drilling technique, osseodensification: an in vitro study
2020
Background Primary stability is an important key determinant of implant osseointegration. We investigated approaches to improve primary implant stability using a new drilling technique termed osseodensification (OD), which was compared with the conventional under-drilling (UD) method utilized for low-density bones. Material and Methods We placed 55 conical internal connection implants in each group, in 30 low-density sections of pig tibia. The implants were placed using twist drill bits in both groups; groups Under Drilling (UD) and Osseodensification (OD) included bone sections subjected to conventional UD and OD drilling, respectively. Before placing the implants, we randomized the bone s…
Akadēmisko un vispārīgo vārdu biežuma salīdzinājums, izmantojot angļu valodas korpusus
2015
Bakalaura darba tēma veltīta korpusu lingvistikas jomas pētniecībai, lai veiktu biežāk lietoto vārdu salīdzināšanu akadēmiskajā un vispārējā angļu valodā ar teksta korpusu palīdzību. Izvēlētās tēmas aktualitāti nosaka valodniecības un moderno tehnoloģiju mijiedarbība, kā arī nepieciešamība izprast, kā tiek lietota un attīstās valoda. Bakalaura darba mērķis ir analizēt teorētisko literatūru par korpusu lingvistiku, kā arī atšķirības starp akadēmiskās un vispārējās angļu valodas pielietojumu. Pētījuma metodoloģija balstīta uz akadēmiskajā studijām un empīrisku pieeju pētījumam. Pētījuma dati iegūti, izmantojot atbilstošu programmatūru, kā arī analizējot biežāk sastopamos vārdus teksta korpuso…
Effects of electrical stimulation pattern on quadriceps isometric force and fatigue in individuals with spinal cord injury
2015
Introduction Variable frequency trains (VFT) or train combinations have been suggested as useful strategies to offset the rapid fatigue induced by constant frequency trains (CFT) during electrical stimulation. However, most studies have been of short duration with limited functional application in those with spinal cord injury (SCI). We therefore tested force and fatigue in response to VFT, CFT, and combined patterns in strength training-like conditions (6-s contractions). Methods Ten SCI individuals underwent either CFT or VFT patterns until target torque was no longer produced and then switched immediately to the other pattern. Results Target torque was reached more times when VFT was use…