18,538 research outputs found
Correlations in Nuclear Matter
We analyze the nuclear matter correlation properties in terms of the pair
correlation function. To this aim we systematically compare the results for the
variational method in the Lowest Order Constrained Variational (LOCV)
approximation and for the Bruekner-Hartree-Fock (BHF) scheme. A formal link
between the Jastrow correlation factor of LOCV and the Defect Function (DF) of
BHF is established and it is shown under which conditions and approximations
the two approaches are equivalent. From the numerical comparison it turns out
that the two correlation functions are quite close, which indicates in
particular that the DF is approximately local and momentum independent. The
Equations of State (EOS) of Nuclear Matter in the two approaches are also
compared. It is found that once the three-body forces (TBF) are introduced the
two EOS are fairly close, while the agreement between the correlation functions
holds with or without TBF.Comment: 11 figure
AAA gunnermodel based on observer theory
The Luenberger observer theory is used to develop a predictive model of a gunner's tracking response in antiaircraft artillery systems. This model is composed of an observer, a feedback controller and a remnant element. An important feature of the model is that the structure is simple, hence a computer simulation requires only a short execution time. A parameter identification program based on the least squares curve fitting method and the Gauss Newton gradient algorithm is developed to determine the parameter values of the gunner model. Thus, a systematic procedure exists for identifying model parameters for a given antiaircraft tracking task. Model predictions of tracking errors are compared with human tracking data obtained from manned simulation experiments. Model predictions are in excellent agreement with the empirical data for several flyby and maneuvering target trajectories
Benchmark ultra-cool dwarfs in widely separated binary systems
Ultra-cool dwarfs as wide companions to subgiants, giants, white dwarfs and
main sequence stars can be very good benchmark objects, for which we can infer
physical properties with minimal reference to theoretical models, through
association with the primary stars. We have searched for benchmark ultra-cool
dwarfs in widely separated binary systems using SDSS, UKIDSS, and 2MASS. We
then estimate spectral types using SDSS spectroscopy and multi-band colors,
place constraints on distance, and perform proper motions calculations for all
candidates which have sufficient epoch baseline coverage. Analysis of the
proper motion and distance constraints show that eight of our ultra-cool dwarfs
are members of widely separated binary systems. Another L3.5 dwarf, SDSS 0832,
is shown to be a companion to the bright K3 giant Eta Cancri. Such primaries
can provide age and metallicity constraints for any companion objects, yielding
excellent benchmark objects. This is the first wide ultra-cool dwarf + giant
binary system identified.Comment: 4 pages, 3 figures, conference, "New Technologies for Probing the
Diversity of Brown Dwarfs and Exoplanets", oral tal
Randomized Revenue Monotone Mechanisms for Online Advertising
Online advertising is the main source of revenue for many Internet firms. A
central component of online advertising is the underlying mechanism that
selects and prices the winning ads for a given ad slot. In this paper we study
designing a mechanism for the Combinatorial Auction with Identical Items (CAII)
in which we are interested in selling identical items to a group of bidders
each demanding a certain number of items between and . CAII generalizes
important online advertising scenarios such as image-text and video-pod
auctions [GK14]. In image-text auction we want to fill an advertising slot on a
publisher's web page with either text-ads or a single image-ad and in
video-pod auction we want to fill an advertising break of seconds with
video-ads of possibly different durations.
Our goal is to design truthful mechanisms that satisfy Revenue Monotonicity
(RM). RM is a natural constraint which states that the revenue of a mechanism
should not decrease if the number of participants increases or if a participant
increases her bid.
[GK14] showed that no deterministic RM mechanism can attain PoRM of less than
for CAII, i.e., no deterministic mechanism can attain more than
fraction of the maximum social welfare. [GK14] also design a
mechanism with PoRM of for CAII.
In this paper, we seek to overcome the impossibility result of [GK14] for
deterministic mechanisms by using the power of randomization. We show that by
using randomization, one can attain a constant PoRM. In particular, we design a
randomized RM mechanism with PoRM of for CAII
Position and energy-resolved particle detection using phonon-mediated microwave kinetic inductance detectors
We demonstrate position and energy-resolved phonon-mediated detection of particle interactions in a silicon substrate instrumented with an array of microwave kinetic inductance detectors (MKIDs). The relative magnitude and delay of the signal received in each sensor allow the location of the interaction to be determined with ≲ 1mm resolution at 30 keV. Using this position information, variations in the detector response with position can be removed, and an energy resolution of σ_E = 0.55 keV at 30 keV was measured. Since MKIDs can be fabricated from a single deposited film and are naturally multiplexed in the frequency domain, this technology can be extended to provide highly pixelized athermal phonon sensors for ∼1 kg scale detector elements. Such high-resolution, massive particle detectors would be applicable to rare-event searches such as the direct detection of dark matter, neutrinoless double-beta decay, or coherent neutrino-nucleus scattering
Critical Temperature tuning of Ti/TiN multilayer films suitable for low temperature detectors
We present our current progress on the design and test of Ti/TiN Multilayer
for use in Kinetic Inductance Detectors (KIDs). Sensors based on
sub-stoichiometric TiN film are commonly used in several applications. However,
it is difficult to control the targeted critical temperature , to maintain
precise control of the nitrogen incorporation process and to obtain a
production uniformity. To avoid these problems we investigated multilayer
Ti/TiN films that show a high uniformity coupled with high quality factor,
kinetic inductance and inertness of TiN. These features are ideal to realize
superconductive microresonator detectors for astronomical instruments
application but also for the field of neutrino physics. Using pure Ti and
stoichiometric TiN, we developed and tested different multilayer configuration,
in term of number of Ti/TiN layers and in term of different interlayer
thicknesses. The target was to reach a critical temperature around
K in order to have a low energy gap and slower recombination time
(i.e. low generation-recombination noise). The results prove that the
superconductive transition can be tuned in the K temperature
range properly choosing the Ti thickness in the nm range, and the
TiN thickness in the nm rang
Ground state of N=Z doubly closed shell nuclei in CBF theory
The ground state properties of N=Z doubly closed shell nuclei are studied
within correlated basis function theory. A truncated version of the Urbana v14
realistic potential, with spin, isospin and tensor components, is adopted,
together with state dependent correlations. Fermi hypernetted chain integral
equation and single operator chain approximation are used to evaluate density,
distribution function and ground state energy of 16O and 40Ca. The results
favourably compare with the available, variational MonteCarlo estimates and
provide a first substantial check of the accuracy of the cluster summation
method for state dependent correlations. We achieve in finite nuclei at least
the same level of accuracy in the treatment of non central interactions and
correlations as in nuclear matter. This opens the way for a microscopic study
of medium heavy nuclei ground state using present days realistic hamiltonians.Comment: 35 pages (LateX) + 3 figures. Phys.Rev.C, in pres
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