122,970 research outputs found
A Theory of Electrodynamic Responses for Bounded Metals: Surface Capacitive Effects
We report a general macroscopic theory for the electrodynamic response of
semi-infinite metals (SIMs). The theory includes the hitherto overlooked
capacitive effects due to the finite spatial extension of a surface. The basic
structure of this theory is independent of the particulars of electron
dynamics. Analytical expressions have been obtained of the charge
density-density response function, which is naturally parsed into two parts.
One of them represents a bulk property while the other a pure surface property.
We apply the theory to study the responses according to several electronic
dynamics models and provide a unified view of their validity and limitations.
The models studied include the local dielectric model (DM), the dispersive
hydrodynamic model (HDM) and specular reflection model (SRM), as well as the
less common semi-classical model (SCM) based on Boltzmann's transport equation.
We show that, in terms of their basic equations, the SRM is an extension of the
HDM, just as the HDM is an extension of the DM. The SCM improves over the SRM
critically through the inclusion of translation symmetry breaking and surface
roughness effects. We then employ the response function to evaluate the
so-called dynamical structure factor, which plays an important role in particle
scattering. As expected, this factor reveals a peak due to the excitation of
surface plasma waves (SPWs). Surprisingly, however, the peak is shown to be
considerably sharper in the SCM than in other models, indicating an incipient
instability of the system according to this model. We also study the
distribution of charges induced by a charged particle grazing over a SIM
surface at constant speed. This distribution is shown to contain model-specific
features that are of immediate experimental interest.Comment: 24 pages, 10 figures, a few more references are added and discussed,
abstract and introduction modified to improve presentation over older
versions, more experimental aspects are discusse
A 10-bit Charge-Redistribution ADC Consuming 1.9 μW at 1 MS/s
This paper presents a 10 bit successive approximation ADC in 65 nm CMOS that benefits from technology scaling. It meets extremely low power requirements by using a charge-redistribution DAC that uses step-wise charging, a dynamic two-stage comparator and a delay-line-based controller. The ADC requires no external reference current and uses only one external supply voltage of 1.0 V to 1.3 V. Its supply current is proportional to the sample rate (only dynamic power consumption). The ADC uses a chip area of approximately 115--225 μm2. At a sample rate of 1 MS/s and a supply voltage of 1.0 V, the 10 bit ADC consumes 1.9 μW and achieves an energy efficiency of 4.4 fJ/conversion-step
Prototyping of the ILC Baseline Positron Target
The ILC positron system uses novel helical undulators to create a powerful
photon beam from the main electron beam. This beam is passed through a titanium
target to convert it into electron-positron pairs. The target is constructed as
a 1 m diameter wheel spinning at 2000 RPM to smear the 1 ms ILC pulse train
over 10 cm. A pulsed flux concentrating magnet is used to increase the positron
capture efficiency. It is cooled to liquid nitrogen temperatures to maximize
the flatness of the magnetic field over the 1 ms ILC pulse train. We report on
prototyping effort on this system.Comment: 7 pages, 9 figures, Proceedings of the International Workshop on
Future Linear Colliders, Granada Spain, 26-30 September 201
The Submillimeter Properties of the 1 Ms Chandra Deep Field North X-ray Sample
We present submillimeter observations for 136 of the 370 X-ray sources
detected in the 1 Ms exposure of the Chandra Deep Field North. Ten of the X-ray
sources are significantly detected in the submillimeter. The average X-ray
source in the sample has a significant 850 micron flux of 1.69+/-0.27 mJy. This
value shows little dependence on the 2-8 keV flux from 5e-16 erg/cm^2/s to
1e-14 erg/cm^2/s. The ensemble of X-ray sources contribute about 10% of the
extragalactic background light at 850 microns. The submillimeter excess is
found to be strongest in the optically faint X-ray sources that are also seen
at 20 cm, which is consistent with these X-ray sources being obscured and at
high redshift (z>1).Comment: 5 pages, submitted to The Astrophysical Journal Letter
Ultra-thin clay layers facilitate seismic slip in carbonate faults
Many earthquakes propagate up to the Earth's surface producing surface ruptures. Seismic slip propagation is facilitated by along-fault low dynamic frictional resistance, which is controlled by a number of physico-chemical lubrication mechanisms. In particular, rotary shear experiments conducted at seismic slip rates (1 ms(-1)) show that phyllosilicates can facilitate co-seismic slip along faults during earthquakes. This evidence is crucial for hazard assessment along oceanic subduction zones, where pelagic clays participate in seismic slip propagation. Conversely, the reason why, in continental domains, co-seismic slip along faults can propagate up to the Earth's surface is still poorly understood. We document the occurrence of micrometer-thick phyllosilicate-bearing layers along a carbonate-hosted seismogenic extensional fault in the central Apennines, Italy. Using friction experiments, we demonstrate that, at seismic slip rates (1 ms(-1)), similar calcite gouges with pre-existing phyllosilicate-bearing (clay content ≤3 wt.%) micro-layers weaken faster than calcite gouges or mixed calcite-phyllosilicate gouges. We thus propose that, within calcite gouge, ultra-low clay content (≤3 wt.%) localized along micrometer-thick layers can facilitate seismic slip propagation during earthquakes in continental domains, possibly enhancing surface displacement
Compartmental analysis of dynamic nuclear medicine data: models and identifiability
Compartmental models based on tracer mass balance are extensively used in
clinical and pre-clinical nuclear medicine in order to obtain quantitative
information on tracer metabolism in the biological tissue. This paper is the
first of a series of two that deal with the problem of tracer coefficient
estimation via compartmental modelling in an inverse problem framework.
Specifically, here we discuss the identifiability problem for a general
n-dimension compartmental system and provide uniqueness results in the case of
two-compartment and three-compartment compartmental models. The second paper
will utilize this framework in order to show how non-linear regularization
schemes can be applied to obtain numerical estimates of the tracer coefficients
in the case of nuclear medicine data corresponding to brain, liver and kidney
physiology
The S2 VLBI Correlator: A Correlator for Space VLBI and Geodetic Signal Processing
We describe the design of a correlator system for ground and space-based
VLBI. The correlator contains unique signal processing functions: flexible LO
frequency switching for bandwidth synthesis; 1 ms dump intervals, multi-rate
digital signal-processing techniques to allow correlation of signals at
different sample rates; and a digital filter for very high resolution
cross-power spectra. It also includes autocorrelation, tone extraction, pulsar
gating, signal-statistics accumulation.Comment: 44 pages, 13 figure
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