3,872 research outputs found
Primordial Non-Gaussianity in the Forest: 3D Bispectrum of Ly-alpha Flux Spectra Along Multiple Lines of Sight
We investigate the possibility of constraining primordial non-Gaussianity
using the 3D bispectrum of Ly-alpha forest. The strength of the quadratic
non-Gaussian correction to an otherwise Gaussian primordial gravitational field
is assumed to be dictated by a single parameter fnl. We present the first
prediction for bounds on fnl using Ly-alpha flux spectra along multiple lines
of sight. The 3D Ly- transmitted flux field is modeled as a biased
tracer of the underlying matter distribution sampled along 1D skewers
corresponding to quasars sight lines. The precision to which fnl can be
constrained depends on the survey volume, pixel noise and aliasing noise
(arising from discrete sampling of the density field). We consider various
combinations of these factors to predict bounds on fnl. We find that in an
idealized situation of full sky survey and negligible Poisson noise one may
constrain fnl ~ 23 in the equilateral limit. Assuming a Ly-alpha survey
covering large parts of the sky (k_{min} = 8 * 10^{-4} Mpc^{-1}) and with a
quasar density of \bar n = 5 * 10^{-3} Mpc^{-2} it is possible to constrain fnl
~ 100 for equilateral configurations. The possibility of measuring fnl at a
precision comparable to LSS studies maybe useful for joint constraining of
inflationary scenarios using different data sets.Comment: 4 pages, 1 figure, 1 table. Accepted for publication in Physical
Review Letter
San Francisco Bay Area KIPP Schools: A Study of Early Implementation and Achievement: Final Report
Examines the achievement results and operations of five Knowledge Is Power Program middle schools to assess the program's effectiveness, the role of leadership, implementation of the KIPP culture, design of curricula and instruction, and lessons learned
PPM demodulation: On approaching fundamental limits of optical communications
We consider the problem of demodulating M-ary optical PPM (pulse-position
modulation) waveforms, and propose a structured receiver whose mean probability
of symbol error is smaller than all known receivers, and approaches the quantum
limit. The receiver uses photodetection coupled with optimized phase-coherent
optical feedback control and a phase-sensitive parametric amplifier. We present
a general framework of optical receivers known as the conditional pulse nulling
receiver, and present new results on ultimate limits and achievable regions of
spectral versus photon efficiency tradeoffs for the single-spatial-mode
pure-loss optical communication channel.Comment: 5 pages, 6 figures, IEEE ISIT, Austin, TX (2010
San Francisco Bay Area KIPP Schools: A Study of Early Implementation
Measures how well five San Francisco Bay Area schools have implemented the goals of the Knowledge Is Power Program during the first year of a three-year initiative to prepare underserved urban youth for college
Measurement and Modeling of Infrared Nonlinear Absorption Coefficients and Laser-induced Damage Thresholds in Ge and GaSb
Using a simultaneous fitting technique to extract nonlinear absorption coefficients from data at two pulse widths, we measure two-photon and free-carrier absorption coefficients for Ge and GaSb at 2.05 and 2.5 μm for the first time, to our knowledge. Results agreed well with published theory. Single-shot damage thresholds were also measured at 2.5 μm and agreed well with modeled thresholds using experimentally determined parameters including nonlinear absorption coefficients and temperature dependent linear absorption. The damage threshold for a single-layer Al2O3 anti-reflective coating on Ge was 55% or 35% lower than the uncoated threshold for picosecond or nanosecond pulses, respectively
Self-monitoring Practices, Attitudes, and Needs of Individuals with Bipolar Disorder: Implications for the Design of Technologies to Manage Mental Health
Objective To understand self-monitoring strategies used independently of clinical treatment by individuals with bipolar disorder (BD), in order to recommend technology design principles to support mental health management.
Materials and Methods Participants with BD (N = 552) were recruited through the Depression and Bipolar Support Alliance, the International Bipolar Foundation, and WeSearchTogether.org to complete a survey of closed- and open-ended questions. In this study, we focus on descriptive results and qualitative analyses.
Results Individuals reported primarily self-monitoring items related to their bipolar disorder (mood, sleep, finances, exercise, and social interactions), with an increasing trend towards the use of digital tracking methods observed. Most participants reported having positive experiences with technology-based tracking because it enables self-reflection and agency regarding health management and also enhances lines of communication with treatment teams. Reported challenges stem from poor usability or difficulty interpreting self-tracked data.
Discussion Two major implications for technology-based self-monitoring emerged from our results. First, technologies can be designed to be more condition-oriented, intuitive, and proactive. Second, more automated forms of digital symptom tracking and intervention are desired, and our results suggest the feasibility of detecting and predicting emotional states from patterns of technology usage. However, we also uncovered tension points, namely that technology designed to support mental health can also be a disruptor.
Conclusion This study provides increased understanding of self-monitoring practices, attitudes, and needs of individuals with bipolar disorder. This knowledge bears implications for clinical researchers and practitioners seeking insight into how individuals independently self-manage their condition as well as for researchers designing monitoring technologies to support mental health management
Dust composition and mass-loss return from the luminous blue variable R71 in the LMC
We present an analysis of mid-and far-infrared (IR) spectrum and spectral
energy distribution (SED) of the LBV R71 in the LMC.This work aims to
understand the overall contribution of high-mass LBVs to the total dust-mass
budget of the interstellar medium (ISM) of the LMC and compare this with the
contribution from low-mass asymptotic giant branch (AGB) stars. As a case
study, we analyze the SED of R71. We compiled all the available photometric and
spectroscopic observational fluxes from various telescopes for a wide
wavelength range (0.36 -- 250\,m). We determined the dust composition from
the spectroscopic data, and derived the ejected dust mass, dust mass-loss rate,
and other dust shell properties by modeling the SED of R71. We noted nine
spectral features in the dust shell of R71 by analyzing Spitzer spectroscopic
data. Among these, we identified three new crystalline silicate features. We
computed our model spectrum by using 3D radiative transfer code MCMax. Our
model calculation shows that dust is dominated by amorphous silicates, with
some crystalline silicates, metallic iron, and a very tiny amount of polycyclic
aromatic hydrocarbon (PAH) molecules. The presence of both silicates and PAHs
indicates that the dust has a mixed chemistry. We derived a dust mass of 0.01
M, from which we arrive at a total ejected mass of 5
M. This implies a time-averaged dust mass-loss rate of
2.510 M\,yr with an explosion about 4000 years
ago. We assume that the other five confirmed dusty LBVs in the LMC loose mass
at a similar rate, and estimate the total contribution to the mass budget of
the LMC to be 10 M\,yr, which is comparable to
the contribution by all the AGB stars in the LMC. Based on our analysis on R71,
we speculate that LBVs as a class may be an important dust source in the ISM of
the LMC.Comment: 10 pages, 6 figures, 2 table
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