7,469 research outputs found
Phonons in a Nanoparticle Mechanically Coupled to a Substrate
The discrete nature of the vibrational modes of an isolated nanometer-scale
solid dramatically modifies its low-energy electron and phonon dynamics from
that of a bulk crystal. However, nanocrystals are usually coupled--even if only
weakly--to an environment consisting of other nanocrystals, a support matrix,
or a solid substrate, and this environmental interaction will modify the
vibrational properties at low frequencies. In this paper we investigate the
modification of the vibrational modes of an insulating spherical nanoparticle
caused by a weak {\it mechanical} coupling to a semi-infinite substrate. The
phonons of the bulk substrate act as a bath of harmonic oscillators, and the
coupling to this reservoir shifts and broadens the nanoparticle's modes. The
vibrational density of states in the nanoparticle is obtained by solving the
Dyson equation for the phonon propagator, and we show that environmental
interaction is especially important at low frequencies. As a probe of the
modified phonon spectrum, we consider nonradiative energy relaxation of a
localized electronic impurity state in the nanoparticle, for which good
agreement with experiment is found.Comment: 10 pages, Revte
A History of United States Cannabis Law
Perhaps the best way to understand early-Twenty-First Century state and federal cannabis law in the United States is to examine the relevant history. Justice Oliver Wendell Holmes, Jr.’s statement is apropos: [A] page of history is worth a volume of logic. This article begins by discussing the early history of cannabis and its uses. Next, the article examines the first state and federal marijuana laws. After a brief comparison of alcohol prohibition to cannabis prohibition, this article addresses cannabis laws from the 1920s to the early 1950s. Then, the article takes up the reorganization of the federal drug regulatory bureaucracy since its inception. Addressing the current era of cannabis laws and regulations, this article recounts how marijuana became a Schedule I drug. The discussion then turns to changing social attitudes towards cannabis as reflected in presidential politics and popular culture. Starting with the late-1990s, this article describes the development of state and federal cannabis laws and policies up to the present day
On the shot-noise limit of a thermal current
The noise power spectral density of a thermal current between two macroscopic
dielectric bodies held at different temperatures and connected only at a
quantum point contact is calculated. Assuming the thermal energy is carried
only by phonons, we model the quantum point contact as a mechanical link,
having a harmonic spring potential. In the weak coupling, or weak-link limit,
we find the thermal current analog of the well-known electronic shot-noise
expression.Comment: 4 pages, 1 figur
Cavity-enhanced room-temperature magnetometry using absorption by nitrogen-vacancy centers in diamond
We demonstrate a cavity-enhanced room-temperature magnetic field sensor based
on nitrogen-vacancy centers in diamond. Magnetic resonance is detected using
absorption of light resonant with the 1042 nm spin-singlet transition. The
diamond is placed in an external optical cavity to enhance the absorption, and
significant absorption is observed even at room temperature. We demonstrate a
magnetic field sensitivity of 2.5 nT/sqrt(Hz), and project a photon
shot-noise-limited sensitivity of 70 pT/sqrt(Hz) for a few mW of infrared
light, and a quantum projection-noise-limited sensitivity of 250 fT/sqrt(Hz)
for the sensing volume of 90 um x 90 um 200 um.Comment: main text 5 pages, supplementary material 3 page
Stream network analysis and geomorphic flood plain mapping from orbital and suborbital remote sensing imagery application to flood hazard studies in central Texas
The author has identified the following significant results. Development of a quantitative hydrogeomorphic approach to flood hazard evaluation was hindered by (1) problems of resolution and definition of the morphometric parameters which have hydrologic significance, and (2) mechanical difficulties in creating the necessary volume of data for meaningful analysis. Measures of network resolution such as drainage density and basin Shreve magnitude indicated that large scale topographic maps offered greater resolution than small scale suborbital imagery and orbital imagery. The disparity in network resolution capabilities between orbital and suborbital imagery formats depends on factors such as rock type, vegetation, and land use. The problem of morphometric data analysis was approached by developing a computer-assisted method for network analysis. The system allows rapid identification of network properties which can then be related to measures of flood response
Close companions to Brightest Cluster Galaxies: Support for minor mergers and downsizing
We identify close companions of Brightest Cluster Galaxies (BCGs) for the
purpose of quantifying the rate at which these galaxies grow via mergers. By
exploiting deep photometric data from the CFHTLS, we probe the number of
companions per BCG (Nc) with luminosity ratios down to those corresponding to
potential minor mergers of 20:1. We also measure the average luminosity in
companions per galaxy (Lc). We find that Nc and Lc rise steeply with luminosity
ratio for both the BCGs, and a control sample of other bright, red, cluster
galaxies. The trend for BCGs rises more steeply, resulting in a larger number
of close companions. For companions within 50kpc of a BCG, Nc= 1.38+/-0.14 and
Lc=(2.14+/-0.31)x10^(10)L_sun and for companions within 50kpc of a luminosity
matched control sample of non-BCGs, Nc=0.87+/-0.08 and
Lc=(1.48+/-0.20)x10^(10)L_sun. This suggests that the BCGs are likely to
undergo more mergers compared to otherwise comparable luminous galaxies.
Additionally, compared to a local sample of luminous red galaxies, the more
distant sample presented in this study (with redshifts between 0.15-0.39,)
shows a higher Nc, suggesting the younger and smaller BCGs are still undergoing
hierarchical formation. Using the Millennium Simulations we model and estimate
the level of contamination due to unrelated cluster galaxies. The contamination
by interloping galaxies is 50% within projected separations of 50kpc, but
within 30kpc, 60% of identified companions are real physical companions. We
conclude that the luminosity of bound merger candidates down to luminosity
ratios of 20:1 could be adding as much as 10% to the mass of a typical BCG over
0.5Gyr at redshifts of z~0.3.Comment: 10 pages, 7 figures. Accepted and to be published in MNRA
Infrared catastrophe and tunneling into strongly correlated electron systems: Exact solution of the x-ray edge limit for the 1D electron gas and 2D Hall fluid
In previous work we have proposed that the non-Fermi-liquid spectral
properties in a variety of low-dimensional and strongly correlated electron
systems are caused by the infrared catastrophe, and we used an exact functional
integral representation for the interacting Green's function to map the
tunneling problem onto the x-ray edge problem, plus corrections. The
corrections are caused by the recoil of the tunneling particle, and, in systems
where the method is applicable, are not expected to change the qualitative form
of the tunneling density of states (DOS). Qualitatively correct results were
obtained for the DOS of the 1D electron gas and 2D Hall fluid when the
corrections to the x-ray edge limit were neglected and when the corresponding
Nozieres-De Dominicis integral equations were solved by resummation of a
divergent perturbation series. Here we reexamine the x-ray edge limit for these
two models by solving these integral equations exactly, finding the expected
modifications of the DOS exponent in the 1D case but finding no changes in the
DOS of the 2D Hall fluid with short-range interaction. We also provide, for the
first time, an exact solution of the Nozieres-De Dominicis equation for the 2D
electron gas in the lowest Landau level.Comment: 6 pages, Revte
Wavelet-Based Processing of Angular Measurements: Application to Realistic Display Aspect Simulation
In this paper, we describe a new wavelet-based data processing that performs simultaneously compression and fast multidimensional interpolation of hemispherical angular features. This algorithm is applied for display aspect simulation to allow predicting the rendering of any content on a given display under any illuminations conditions. Such rendering is based on a complex set of data composed of emitting display properties as a function of angle as well as its reflective behavior (BRDF). This record was migrated from the OpenDepot repository service in June, 2017 before shutting down
- …