30,563 research outputs found
Disorder in order: Localization without randomness in a cold-atom system
We present a mapping between the Edwards model of disorder describing the
motion of a single particle subject to randomly-positioned static scatterers
and the Bose polaron problem of a light quantum impurity interacting with a
Bose-Einstein condensate (BEC) of heavy atoms. The mapping offers an
experimental setting to investigate the physics of Anderson localization where,
by exploiting the quantum nature of the BEC, the time evolution of the quantum
impurity emulates the disorder-averaged dynamics of the Edwards model. Valid in
any space dimension, the mapping can be extended to include interacting
particles, arbitrary disorder or confinement, and can be generalized to study
many-body localization. Moreover, the corresponding exactly-solvable disorder
model offers means to benchmark variational approaches used to study polaron
physics. Here, we illustrate the mapping by focusing on the case of an impurity
interacting with a one-dimensional BEC through a contact interaction. While a
simple wave function based on the expansion in the number of bath excitations
misses the localization physics entirely, a coherent state Ansatz combined with
a canonical transformation captures the physics of disorder and Anderson
localization.Comment: 10 pages, 4 figures. Definitive versio
Giant electrocaloric effect around T
We use molecular dynamics with a first-principles-based shell model potential
to study the electrocaloric effect (ECE) in lithium niobate, LiNbO, and
find a giant electrocaloric effect along a line passing through the
ferroelectric transition. With applied electric field, a line of maximum ECE
passes through the zero field ferroelectric transition, continuing along a
Widom line at high temperatures with increasing field, and along the
instability that leads to homogeneous ferroelectric switching below with
an applied field antiparallel to the spontaneous polarization. This line is
defined as the minimum in the inverse capacitance under applied electric field.
We investigate the effects of pressure, temperature and applied electric field
on the ECE. The behavior we observe in LiNbO should generally apply to
ferroelectrics; we therefore suggest that the operating temperature for
refrigeration and energy scavenging applications should be above the
ferroelectric transition region to obtain large electrocaloric response. We
find a relationship among , the Widom line and homogeneous switching that
should be universal among ferroelectrics, relaxors, multiferroics, and the same
behavior should be found under applied magnetic fields in ferromagnets.Comment: 5 page
Time evolution of the Partridge-Barton Model
The time evolution of the Partridge-Barton model in the presence of the
pleiotropic constraint and deleterious somatic mutations is exactly solved for
arbitrary fecundity in the context of a matricial formalism. Analytical
expressions for the time dependence of the mean survival probabilities are
derived. Using the fact that the asymptotic behavior for large time is
controlled by the largest matrix eigenvalue, we obtain the steady state values
for the mean survival probabilities and the Malthusian growth exponent. The
mean age of the population exhibits a power law decayment. Some Monte
Carlo simulations were also performed and they corroborated our theoretical
results.Comment: 10 pages, Latex, 1 postscript figure, published in Phys. Rev. E 61,
5664 (2000
The limits of process: On (re)reading Henri Bergson
This article offers a reading of the work of Henri Bergson as it pertains to organizations through the lens of ideas drawn from critical realism. It suggests an alternative to interpretations based on a stark division between process and realist perspectives. Much of the existing literature presents a rather partial view of Bergson’s work. A review suggests some interesting parallels with themes in critical realism, notably the emergence of mind. Critical realism has a focus on process at its heart, but is also concerned with how the products of such processes become stabilized and form the conditions for action. This suggests that attention might usefully be paid to the relationship between organizational action and the sedimented practices grouped under the heading of ‘routines’. More attention to Bergson’s account of the relationship between instinct, intuition and intelligence provides a link to the social character of thought, something which can be mapped on to Archer’s work on reflexivity and the ‘internal conversation’. This suggests that our analyses need to pay attention to both memory and history, to building and dwelling, rather than the one-sided focus found in some process theory accounts
Functional-renormalization-group approach to strongly coupled Bose-Fermi mixtures in two dimensions
We study theoretically the phase diagram of strongly coupled two-dimensional
Bose-Fermi mixtures interacting with attractive short-range potentials as a
function of the particle densities. We focus on the limit where the size of the
bound state between a boson and a fermion is small compared to the average
interboson separation and develop a functional-renormalization-group approach
that accounts for the bound-state physics arising from the extended
Fr\"{o}hlich Hamiltonian. By including three-body correlations we are able to
reproduce the polaron-to-molecule transition in two-dimensional Fermi gases in
the extreme limit of vanishing boson density. We predict frequency- and
momentum-resolved spectral functions and study the impact of three-body
correlations on quasiparticle properties. At finite boson density, we find that
when the bound-state energy exceeds the Fermi energy by a critical value, the
fermions and bosons can form a fermionic composite with a well-defined Fermi
surface. These composites constitute a Fermi sea of dressed Feshbach molecules
in the case of ultracold atoms while in the case of atomically thin
semiconductors a trion liquid emerges. As the boson density is increased
further, the effective energy gap of the composites decreases, leading to a
transition into a strongly correlated phase where polarons are hybridized with
molecular degrees of freedom. We highlight the universal connection between
two-dimensional semiconductors and ultracold atoms and we discuss perspectives
for further exploring the rich structure of strongly coupled Bose-Fermi
mixtures in these complementary systems.Comment: 28 pages, 12 figure
The diffuse X-ray background spectrum from 3 to 50keV
The spectrum of the extragalactic diffuse X-ray background was measured with the GSFC cosmic X-ray experiment on HEAO-1 for regions of the sky away from known point sources and more than 20 deg from the galactic plane. A total exposure of 80 sq m-sec-sr is available at present. Free-free emission from an optically thin plasma of 40 plus or minus 5 keV provides an excellent description of the observed spectrum from 3 to 50 keV. This spectral shape is confirmed by measurements from 5 separate layers of three independent detectors. With an estimated absolute precision of about 10 percent, the intensity of the emission at 10 keV is 3.2 keV/keV-sq cm-sec-sr, a value consistent with the average of previously reported spectra. No other spectral features, such as iron line emission, are evident. This spectrum is not typical of known extragalactic objects. A uniform hot intergalactic medium of approximately 36 percent of the closure density of the universe would produce such a flux, although non-uniform models indicating less total matter are probably more realistic
Lokasi Penanaman Bawang Merah Lokal Samosir Berdasarkan Ketinggian Tempat Di Daerah Tangkapan Air Danau Toba
Penelitian ini bertujuan untuk menentukan lokasi penanaman bawang merah lokal Samosir berdasarkan ketinggian tempat di Daerah Tangkapan Air Danau Toba. Penelitian ini dilaksanakan di sentra kawasan penanaman bawang merah di daerah sekitaran Danau Toba dengan ketinggian tempat 900 – 2000 meter diatas permukaan laut. Penelitian ini dilaksanakan dengan metode survey yang meliputi studi literatur, penyusunan kuisioner, survey lapangan dan pengolahan data hasil survey lapangan. Hasil penelitian menunjukkan bahwa ketinggian tempat dan produksi bawang merah lokal Samosir berkorelasi negatif, artinya semakin tinggi ketinggian tempat maka produksi akan menurun dengan nilai r = 0.51. Ketinggian tempat yang terbaik untuk budidaya bawang merah lokal Samosir di DTA Danau Toba adalah ketinggian 900 – 1000 m dpl
Comments on Anomaly Cancellations by Pole Subtractions and Ghost Instabilities with Gravity
We investigate some aspects of anomaly cancellation realized by the
subtraction of an anomaly pole, stressing on some of its properties in
superspace. In a local formulation these subtractions can be described in terms
of a physical scalar, an axion and related ghosts. They appear to be necessary
for the unitarization of the theory in the ultraviolet, but they may generate
an infrared instability of the corresponding effective action, signalled by
ghost condensation. In particular the subtraction of the superanomaly multiplet
by a pole in superspace is of dubious significance, due to the different nature
of the chiral and conformal anomalies. In turn, this may set more stringent
constraints on the coupling of supersymmetric theories to gravity.Comment: 18 pages. Revised version. To appear in "Classical and Quantum
Gravity
Consequences of wall stiffness for a beta-soft potential
Modifications of the infinite square well E(5) and X(5) descriptions of
transitional nuclear structure are considered. The eigenproblem for a potential
with linear sloped walls is solved. The consequences of the introduction of
sloped walls and of a quadratic transition operator are investigated.Comment: RevTeX 4, 8 pages, as published in Phys. Rev.
Fertility and well-being in the italian regions
We analyse the association between fertility rates and well-being in the Italian regions in the period 2012-2017. Well-being is measured by the indicators of Equitable and Sustainable Well-being (BES), collected by ISTAT since 2013 with the aim of evaluating the economic, social and environmental development of the society through measurement of citizens’ life quality. We expect that the regions performing better in terms of well-being conditions are also those with the highest levels of fertility. Both graphical and panel data regression analyses support our main hypothesis, but also reveal that in different clusters of regions the intensity and direction of the relationship significantly change. Our results also stress the need of taking the different domains of well-being into account while explaining reproductive behaviour of resident population at territorial level
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