Ultraslow Electron Spin Dynamics in GaAs Quantum Wells Probed by Optically Pumped NMR

Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum well samples near the fractional quantum Hall effect ground state nu=1/3. Below 0.5K, the spectra provide evidence that spin-reversed charged excitations of the nu=1/3 ground state are localized over the NMR time scale of ~40 microseconds. Furthermore, by varying NMR pulse parameters, the electron spin temperature (as measured by the Knight shift) could be driven above the lattice temperature, which shows that the value of the electron spin-lattice relaxation time lies between 100 microseconds and 500 milliseconds at nu=1/3.Comment: 6 pages (REVTEX), 6 eps figures embedded in text; published version; minor changes to match published versio

Using Camtasia To Create Video Tutorials: Students As Academic Partners Project Report.

The aim of this project was to create a series of online video tutorials for a Level 4 module (COMP1342 – Creative Computing). For various reasons, students may miss a seminar or prefer a different learning style than is presented during a specific Computing session. Thus, some students may benefit from having a series of online tutorials that present similar information presented in a specific seminar. Web links to the videos can be posted to Blackboard where students may view the online tutorials at their convenience. The project was led by a Computing tutor who supervised a Computing student who created six weeks of online video-based tutorials for the COMP1342 module. The tutorials were created with Camtasia, a software product which records both the computer screen activity and audio from the speaker. This can be especially valuable for creating tutorials of computer-based lessons. Results of the first four weeks where the content was available showed that an average of 21% of students did watch the video tutorials. Several students expressed the appreciation of having tutorials that they could watch at their convenience, especially if they did not fully understand the lesson presented in the regular class seminar

A Study of Global Hospital Websites for Accessibility Compliance

The research investigated accessibility problems of 160 hospital websites, located in 16 countries across 4 continents using Tawdis accessibility software tool. Statistics were analyzed from two layers of WCAG guidance, levels A and AAA, revealing a high incidence of problems at both levels. Asian hospital websites had the greatest number of accessibility issues, although the vast majority of sites in all countries had some type of issues. Only two of the hospital websites included in the study were fully Level A compliant. The study concludes that hospitals are not doing an adequate job of complying with accessibility standards or government legislation, thus depriving many of their web customers the ability to fully use the sites

Управление затратами на полиграфических предприятиях с применением алгоритмов «Экономного производства»

Проведено дослідження різних алгоритмів концепції «Економні виробництва», проаналізовано результати практичного застосування алгоритму, адаптованого до вітчизняних підприємств в умовах ЗАТ «Віпол».In the conditions of market economy and economic crisis in the country entities a transformation of priorities, among which one of the first places is making a profit as a result of lower production costs, efficient use of inputs. The essence of the concept of «economical production». The principles and its various algorithms what can be used by companies in countries with developed market economies. The analysis of introduction of algorithm of «economy production», adapted to the domestic enterprises, JSC «Vipol» whose results showed the effectiveness of such control system of cost management in printing companies.Проведено исследование различных алгоритмов концепции «экономного производства», проанализированы результаты практического применения алгоритма, адаптированного к отечественным предприятиям в условиях ЗАО «Випол»

EEG Slow Waves in Traumatic Brain Injury: Convergent Findings in Mouse and Man

OBJECTIVE: Evidence from previous studies suggests that greater sleep pressure, in the form of EEG-based slow waves, accumulates in specific brain regions that are more active during prior waking experience. We sought to quantify the number and coherence of EEG slow waves in subjects with mild traumatic brain injury (mTBI). METHODS: We developed a method to automatically detect individual slow waves in each EEG channel, and validated this method using simulated EEG data. We then used this method to quantify EEG-based slow waves during sleep and wake states in both mouse and human subjects with mTBI. A modified coherence index that accounts for information from multiple channels was calculated as a measure of slow wave synchrony. RESULTS: Brain-injured mice showed significantly higher theta:alpha amplitude ratios and significantly more slow waves during spontaneous wakefulness and during prolonged sleep deprivation, compared to sham-injured control mice. Human subjects with mTBI showed significantly higher theta:beta amplitude ratios and significantly more EEG slow waves while awake compared to age-matched control subjects. We then quantified the global coherence index of slow waves across several EEG channels in human subjects. Individuals with mTBI showed significantly less EEG global coherence compared to control subjects while awake, but not during sleep. EEG global coherence was significantly correlated with severity of post-concussive symptoms (as assessed by the Neurobehavioral Symptom Inventory scale). CONCLUSION AND IMPLICATIONS: Taken together, our data from both mouse and human studies suggest that EEG slow wave quantity and the global coherence index of slow waves may represent a sensitive marker for the diagnosis and prognosis of mTBI and post-concussive symptoms

EEG Slow Waves in Traumatic Brain Injury: Convergent Findings in Mouse and Man

OBJECTIVE: Evidence from previous studies suggests that greater sleep pressure, in the form of EEG-based slow waves, accumulates in specific brain regions that are more active during prior waking experience. We sought to quantify the number and coherence of EEG slow waves in subjects with mild traumatic brain injury (mTBI). METHODS: We developed a method to automatically detect individual slow waves in each EEG channel, and validated this method using simulated EEG data. We then used this method to quantify EEG-based slow waves during sleep and wake states in both mouse and human subjects with mTBI. A modified coherence index that accounts for information from multiple channels was calculated as a measure of slow wave synchrony. RESULTS: Brain-injured mice showed significantly higher theta:alpha amplitude ratios and significantly more slow waves during spontaneous wakefulness and during prolonged sleep deprivation, compared to sham-injured control mice. Human subjects with mTBI showed significantly higher theta:beta amplitude ratios and significantly more EEG slow waves while awake compared to age-matched control subjects. We then quantified the global coherence index of slow waves across several EEG channels in human subjects. Individuals with mTBI showed significantly less EEG global coherence compared to control subjects while awake, but not during sleep. EEG global coherence was significantly correlated with severity of post-concussive symptoms (as assessed by the Neurobehavioral Symptom Inventory scale). CONCLUSION AND IMPLICATIONS: Taken together, our data from both mouse and human studies suggest that EEG slow wave quantity and the global coherence index of slow waves may represent a sensitive marker for the diagnosis and prognosis of mTBI and post-concussive symptoms

Spectroscopic Evidence for the Localization of Skyrmions near Nu=1 as T->0

Optically pumped nuclear magnetic resonance measurements of Ga-71 spectra were carried out in an n-doped GaAs/Al0.1Ga0.9As multiple quantum well sample near the integer quantum Hall ground state Nu=1. As the temperature is lowered (down to T~0.3 K), a ``tilted plateau'' emerges in the Knight shift data, which is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and Nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional skyrmions.Comment: 4 pages (REVTEX), 5 eps figures embedded in text, published versio

Cluster formation restricts dynamic nuclear polarization of xenon in solid mixtures

During dynamic nuclear polarization (DNP) at 1.5 K and 5 T, (129)Xe nuclear magnetic resonance (NMR) spectra of a homogeneous xenon/1-propanol/trityl-radical solid mixture exhibit a single peak, broadened by (1)H neighbors. A second peak appears upon annealing for several hours at 125 K. Its characteristic width and chemical shift indicate the presence of spontaneously formed pure Xe clusters. Microwave irradiation at the appropriate frequencies can bring both peaks to either positive or negative polarization. The peculiar time evolution of (129)Xe polarization in pure Xe clusters during DNP can be modelled as an interplay of spin diffusion and T(1) relaxation. Our simple spherical-cluster model offers a sensitive tool to evaluate major DNP parameters in situ, revealing a severe spin-diffusion bottleneck at the cluster boundaries and a significant sample overheating due to microwave irradiation. Subsequent DNP system modifications designed to reduce the overheating resulted in four-fold increase of (129)Xe polarization, from 5.3% to 21%

Optically Pumped NMR Measurements of the Electron Spin Polarization in GaAs Quantum Wells near Landau Level Filling Factor nu=1/3

The Knight shift of Ga-71 nuclei is measured in two different electron-doped multiple quantum well samples using optically pumped NMR. These data are the first direct measurements of the electron spin polarization, P(nu,T)=/max, near nu=1/3. The P(T) data at nu=1/3 probe the neutral spin-flip excitations of a fractional quantum Hall ferromagnet. In addition, the saturated P(nu) drops on either side of nu=1/3, even in a Btot=12 Tesla field. The observed depolarization is quite small, consistent with an average of about 0.1 spin-flips per quasihole (or quasiparticle), a value which does not appear to be explicable by the current theoretical understanding of the FQHE near nu=1/3.Comment: 4 pages (REVTEX), 5 eps figures embedded in text; minor changes, published versio