Floquet Analysis of Atom Optics Tunneling Experiments

Dynamical tunneling has been observed in atom optics experiments by two groups. We show that the experimental results are extremely well described by time-periodic Hamiltonians with momentum quantized in units of the atomic recoil. The observed tunneling has a well defined period when only two Floquet states dominate the dynamics. Beat frequencies are observed when three Floquet states dominate. We find frequencies which match those observed in both experiments. The dynamical origin of the dominant Floquet states is identified.Comment: Accepted in Physical Review

Does biofeedback increase gait velocity in children with cerebral palsy?

Objective: The objective of this selective EBM review is to determine whether or not “Does biofeedback increase gait velocity in children with cerebral palsy (CP)?”. Study Design: A systematic review of three randomized control trials (RCTs) published between 2014 and 2019. Data Sources: All three RCTs were found using PubMed. Each article was published in English in peer reviewed journals and selected based on their applicability to the clinical question, provide a new technique in CP rehabilitation, and include patient-oriented outcomes (POEMS). Outcome Measured: The outcome measured was gait velocity before and after treatment using Tekscan software, 3D motion analysis system, and 10-meter walk test. The mean change from baseline was calculated once the treatment was received for both the control and study groups. Results: In the RCT by Hussein et al., biofeedback increased gait velocity as compared to the control group (p = 0.03), indicated by a mean change from baseline of -9.6 cm/second in the study group versus -2.69 cm/second in the control group. In the RCT by Elnaggar, biofeedback increased gait velocity as compared to the control group (p = 0.042), indicated by a mean change from baseline of 6.235 m/minute in the study group versus 1.73 m/minute in the control group. In the RCT by Cho et al., biofeedback increased gait velocity as compared to the control group (p = 0.001), indicated by a mean change from baseline of 0.5 m/second in the study group versus 0.2 m/second in the control group. Conclusion: All three studies demonstrated that biofeedback significantly increased gait velocity in children with CP. This indicates that biofeedback is an effective treatment method for gait training in children with CP. Future studies should focus on expanding generalizability and ease of access to biofeedback options

How active cholesterol coordinates cell cholesterol homeostasis: Test of a hypothesis

How do cells coordinate the diverse elements that regulate their cholesterol homeostasis? Our model postulates that membrane cholesterol forms simple complexes with bilayer phospholipids. The phospholipids in the plasma membrane are of high affinity; consequently, they are fully complexed with the sterol. This sets the resting level of plasma membrane cholesterol. Cholesterol in excess of the stoichiometric equivalence point of these complexes has high chemical activity; we refer to it as active cholesterol. It equilibrates with the low affinity phospholipids in the intracellular membranes where it serves as a negative feedback signal to a manifold of regulatory proteins that rein in ongoing cholesterol accretion. We tested the model with a review of the literature regarding fourteen homeostatic proteins in enterocytes. It provided strong albeit indirect support for the following hypothesis. Active cholesterol inhibits cholesterol uptake and biosynthesis by suppressing both the expression and the activity of the gene products activated by SREBP-2; namely, HMGCR, LDLR and NPC1L1. It also reduces free cell cholesterol by serving as the substrate for its esterification by ACAT and for the synthesis of side-chain oxysterols, 27-hydroxycholesterol in particular. The oxysterols drive cholesterol depletion by promoting the destruction of HMGCR and stimulating sterol esterification as well as the activation of LXR. The latter fosters the expression of multiple homeostatic proteins, including four transporters for which active cholesterol is the likely substrate. By nulling active cholesterol, the manifold maintains the cellular sterol at its physiologic set point

Magnetometer suitable for Earth field measurement based on transient atomic response

We describe the development of a simple atomic magnetometer using $^{87}$Rb vapor suitable for Earth magnetic field monitoring. The magnetometer is based on time-domain determination of the transient precession frequency of the atomic alignment around the measured field. A sensitivity of 1.5 nT/$\sqrt{Hz}$ is demonstrated on the measurement of the Earth magnetic field in the laboratory. We discuss the different parameters determining the magnetometer precision and accuracy and predict a sensitivity of 30 pT/$\sqrt{Hz}$Comment: 6 pages, 5 figure

A Monte Carlo Method for Modeling Thermal Damping: Beyond the Brownian-Motion Master Equation

The "standard" Brownian motion master equation, used to describe thermal damping, is not completely positive, and does not admit a Monte Carlo method, important in numerical simulations. To eliminate both these problems one must add a term that generates additional position diffusion. He we show that one can obtain a completely positive simple quantum Brownian motion, efficiently solvable, without any extra diffusion. This is achieved by using a stochastic Schroedinger equation (SSE), closely analogous to Langevin's equation, that has no equivalent Markovian master equation. Considering a specific example, we show that this SSE is sensitive to nonlinearities in situations in which the master equation is not, and may therefore be a better model of damping for nonlinear systems.Comment: 6 pages, revtex4. v2: numerical results for a nonlinear syste

Speculative Enthusiasm: An Examination of the Role of Risk Appetite within the Framework of Minsky's Financial Instability Hypothesis

Thesis advisor: Harold PetersenMinsky developed a Financial Instability Hypothesis which sought to find an endogenous explanation for a modern economy’s vulnerability to crashes. Specifically, he investigated the ways in which the financial structures of a modern economy might contribute to its instability. The hypothesis rests upon the twin assertions that some financial arrangements are more dangerous than others, and that during economic booms, investors’ incentives are altered to favor these more dangerous arrangements. Essentially, in good times, the profit-seeking motive of investors overrides a diminished risk aversion, as memories of losses fade into the past. This paper empirically tests Minsky’s second assertion, by using econometric techniques to analyze the relationship between risk appetite and market returns. Spreads between the yields of bonds of different credit qualities are used as a proxy for wider investor sentiment toward risk. Regressions demonstrate that changes in risk appetite can be explained at least in part by historical market returns. Such a finding supports Minsky’s proposal that incentives of investors change in response to varying market conditions. It further implies that regulatory authorities might examine the level of risk appetite to determine whether increases in asset prices indicate the formation of speculative bubbles or are rather reflecting developments in the fundamentals underlying said assets.Thesis (BA) — Boston College, 2010.Submitted to: Boston College. College of Arts and Sciences.Discipline: Economics Honors Program.Discipline: College Honors Program.Discipline: Economics

Diffusion weighted imaging, apparent diffusion coefficient maps and stroke etiology

Objective : In acute ischemic stroke, the number and distribution of lesions on diffusion weighted imaging (DWI) have been shown to give clues to the underlying pathogenetic mechanisms. The objective of this study was to determine whether lesion features on DWI differ between stroke due to large artery atherosclerosis (LAA) and cardioembolism (CE), and to assess the role of apparent diffusion coefficient maps (ADC). Methods : We retrospectively studied 83 consecutive patients with stroke caused by either LAA (n = 40) or cardioembolism (n = 43). DWI lesions were characterized by number, size, distribution (i. e. lesion pattern) and signal intensity on ADC maps. In part A, all hyperintense DWI lesions regardless of their ADC were compared. In part B, only hyperintense DWI lesions with hypointense appearance on ADC maps (i. e. acute lesions) were assessed. Results : Part A: The frequency of multiple hyperintense DWI lesions (LAA: 28/40, CE: 21/43; p 1 circulation (i. e. anterior plus posterior or bilateral anterior circulations) was present in 5 LAA-patients (13 %) and 4 CE-patients (9 %). Lesion size did not differ between LAA-stroke (35.1 ± 33.7 mm) and CE-stroke (35.4 ± 27.8 mm). Part B: Multiple hyperintense DWI lesions with low ADC occurred in 23/40 LAA-patients and in 15/43 CE-patients (p 1 circulation occurred only in CE-stroke (n = 3; 7%) and never in LAA-stroke. Conclusions : (1) Multiple ischemic lesions occur significantly more often in LAA-stroke than in CE-stroke. (2) ADC maps are important in the comparison of DWI lesion patterns; DWI lesions in > 1 circulation can only be assigned to a cardioembolic etiology if they appear hypointense on ADC map

Narrow structure in the coherent population trapping resonances in rubidium and Rayleigh scattering

The measurement of the coherent-population-trapping (CPT) resonances in uncoated Rb vacuum cells has shown that the shape of the resonances is different in different cells. In some cells the resonance has a complex shape - a narrow Lorentzian structure, which is not power broadened, superimposed on the power broadened CPT resonance. The results of the performed investigations on the fluorescence angular distribution are in agreement with the assumption that the narrow structure is a result of atom interaction with Rayleigh scattering light. The results are interesting for indication of the vacuum cleanness of the cells and building of magnetooptical sensors