Telespectrograph Patent

Telespectrograph for analyzing upper atmosphere by tracking bodies reentering atmosphere at high velocitie

Quantum dynamics of the avian compass

The ability of migratory birds to orient relative to the Earth's magnetic field is believed to involve a coherent superposition of two spin states of a radical electron pair. However, the mechanism by which this coherence can be maintained in the face of strong interactions with the cellular environment has remained unclear. This Letter addresses the problem of decoherence between two electron spins due to hyperfine interaction with a bath of spin 1/2 nuclei. Dynamics of the radical pair density matrix are derived and shown to yield a simple mechanism for sensing magnetic field orientation. Rates of dephasing and decoherence are calculated ab initio and found to yield millisecond coherence times, consistent with behavioral experiments

Cartesian Bicategories II

The notion of cartesian bicategory, introduced by Carboni and Walters for locally ordered bicategories, is extended to general bicategories. It is shown that a cartesian bicategory is a symmetric monoidal bicategory

Decoherence of a quantum memory coupled to a collective spin bath

We study the quantum dynamics of a single qubit coupled to a bath of interacting spins as a model for decoherence in solid state quantum memories. The spin bath is described by the Lipkin-Meshkov-Glick model and the bath spins are subjected to a transverse magnetic field. We investigate the qubit interacting via either an Ising- or an XY-type coupling term to subsets of bath spins of differing size. The large degree of symmetry of the bath allows us to find parameter regimes where the initial qubit state is revived at well defined times after the qubit preparation. These times may become independent of the bath size for large baths and thus enable faithful qubit storage even in the presence of strong coupling to a bath. We analyze a large range of parameters and identify those which are best suited for quantum memories. In general we find that a small number of links between qubit and bath spins leads to less decoherence and that systems with Ising coupling between qubit and bath spins are preferable.Comment: 13 pages, 8 figure

Photoluminescence quantum efficiency of dense silicon nanocrystal ensembles in SiO2

The photoluminescence decay characteristics of silicon nanocrystals in dense ensembles fabricated by ion implantation into silicon dioxide are observed to vary in proportion to the calculated local density of optical states. A comparison of the experimental 1/e photoluminescence decay rates to the expected spontaneous emission rate modification yields values for the internal quantum efficiency and the intrinsic radiative decay rate of silicon nanocrystals. A photoluminescence quantum efficiency as high as 59%±9% is found for nanocrystals emitting at 750 nm at low excitation power. A power dependent nonradiative decay mechanism reduces the quantum efficiency at high pump intensity

Sleep disturbance and serum ferritin levels associate with high impulsivity and impulse control disorders in male Parkinson\u27s Disease patients

Impulse control disorders (ICDs) occur in a subset of Parkinson’s disease (PD) patients on dopaminergic medications however there are currently no reliable markers to identify patients at risk. Sleep disturbances are more common in patients with an ICD. Serum ferritin levels have been associated with PD disease stage and progression, but have not previously been associated with impulsivity levels. The objective of this study was to determine if serum ferritin levels and sleep disturbance are associated with high traits of impulsivity and ICD in a cohort of PD patients attending a movement disorders clinic. This study assessed impulsiveness in 87 PD patients using the Barratt Impulsiveness Scale. Severity of sleep disturbance was determined using the sleep-related items of the MDS-UPDRS. Serum ferritin, iron and transferrin levels were measured in patients, as well as 36 age-matched healthy controls. Serum ferritin levels were significantly elevated in male PD patients in the high impulsivity group compared to patients in the low (p=.022) and normal range groups (p=.024) and showed a linear increase across the three groups. Sleep disturbance also demonstrated a linear trend, which was most severe in the high impulsivity group (p=.030). A subgroup of 11 male PD patients who fulfilled the DSM-5 criteria for an ICD had significantly higher ferritin levels and more severe sleep disturbance when compared with the remaining male PD cohort. Serum ferritin levels and sleep disturbance severity are highlighted as potential markers for abnormal impulsivity and ICD in PD patients

Development program for 35 watt traveling-wave tube space amplifier Final report, 30 Jun. 1967 - 30 Sep. 1969

Development of 35-watt, S band, traveling wave tube amplifier for Saturn 5 instrument uni

Neutron spin-echo study of the critical dynamics of spin-5/2 antiferromagnets in two and three dimensions

We report a neutron spin-echo study of the critical dynamics in the $S=5/2$ antiferromagnets MnF$_2$ and Rb$_2$MnF$_4$ with three-dimensional (3D) and two-dimensional (2D) spin systems, respectively, in zero external field. Both compounds are Heisenberg antiferromagnets with a small uniaxial anisotropy resulting from dipolar spin-spin interactions, which leads to a crossover in the critical dynamics close to the N\'eel temperature, $T_N$. By taking advantage of the $\mu\text{eV}$ energy resolution of the spin-echo spectrometer, we have determined the dynamical critical exponents $z$ for both longitudinal and transverse fluctuations. In MnF$_2$, both the characteristic temperature for crossover from 3D Heisenberg to 3D Ising behavior and the exponents $z$ in both regimes are consistent with predictions from the dynamical scaling theory. The amplitude ratio of longitudinal and transverse fluctuations also agrees with predictions. In Rb$_2$MnF$_4$, the critical dynamics crosses over from the expected 2D Heisenberg behavior for $T\gg T_N$ to a scaling regime with exponent $z = 1.387(4)$, which has not been predicted by theory and may indicate the influence of long-range dipolar interactions

Charter Schools and the Road to College Readiness: The Effects on College Preparation, Attendance and Choice

The analysis here focuses on Boston's charter high schools. For the purpose of this report, an analysis of high schools is both a necessity and a virtue. It is necessary to study high schools because most students applying to charters in earlier grades are not yet old enough to generate data on postsecondary outcomes. Charter high schools are also of substantial policy interest: a growing body of research argues that high school may be too late for cost-effective human capital interventions. Indeed, impact analyses of interventions for urban youth have mostly generated disappointing results.This report is interested in ascertaining whether charter schools, which in Massachusetts are largely budget-neutral, can have a substantial impact on the life course of affected students. The set of schools studied here comes from an earlier investigation of the effects of charter attendance in Boston on test scores.The high schools from the earlier study, which enroll the bulk of charter high school students in Boston, generate statistically and socially significant gains on state assessments in the 10th grade. This report questions whether these gains are sustained

Who Benefits from KIPP?

The nation's largest charter management organization is the Knowledge is Power Program (KIPP). KIPP schools are emblematic of the No Excuses approach to public education, a highly standardized and widely replicated charter model that features a long school day, an extended school year, selective teacher hiring, strict behavior norms, and a focus on traditional reading and math skills. No Excuses charter schools are sometimes said to focus on relatively motivated high achievers at the expense of students who are most diffiult to teach, including limited English proficiency (LEP) and special education (SPED) students, as well as students with low baseline achievement levels. We use applicant lotteries to evaluate the impact of KIPP Academy Lynn, a KIPP school in Lynn, Massachusetts that typifies the KIPP approach. Our analysis focuses on special needs students that may be underserved. The results show average achievement gains of 0.36 standard deviations in math and 0.12 standard deviations in reading for each year spent at KIPP Lynn, with the largest gains coming from the LEP, SPED, and low-achievement groups. The average reading gains are driven almost completely by SPED and LEP students, whose reading scores rise by roughly 0.35 standard deviations for each year spent at KIPP Lynn.human capital, charter schools, achievement