2,305 research outputs found
An atomic boson sampler
A boson sampler implements a restricted model of quantum computing. It is
defined by the ability to sample from the distribution resulting from the
interference of identical bosons propagating according to programmable,
non-interacting dynamics. Here, we demonstrate a new combination of tools for
implementing boson sampling using ultracold atoms in a two-dimensional,
tunnel-coupled optical lattice. These tools include fast and programmable
preparation of large ensembles of nearly identical bosonic atoms
( indistinguishability) by means of rearrangement with
optical tweezers and high-fidelity optical cooling, propagation for variable
evolution time in the lattice with low loss (, independent of
evolution time), and high fidelity detection of the atom positions after their
evolution (typically ). With this system, we study specific
instances of boson sampling involving up to atoms distributed among sites in the lattice. Direct verification of a given boson sampling
distribution is not feasible in this regime. Instead, we introduce and perform
targeted tests to determine the indistinguishability of the prepared atoms, to
characterize the applied family of single particle unitaries, and to observe
expected bunching features due to interference for a large range of atom
numbers. When extended to interacting systems, our work demonstrates the core
capabilities required to directly assemble ground and excited states in
simulations of various Hubbard models.Comment: 20 pages, 7 figures (main text and methods); 8 pages, 2 figures
(supplemental materials
Phase Transitions in Chemisorbed Systems
Contains reports on six research projects.Joint Services Electronics Program (Contract DAAG29-83-K-0003
Signals of the cosmological reionization in the radio sky through C and O fine structure lines
We study the excitation of fine structure levels of C I, C II and O I by
ultraviolet (UV) photons around strong UV sources which are also ionizing
sources of the cosmological reionization at redshift of . The
evolutions of ionized regions around a point source are calculated by solving
rate equations for non-equilibrium chemistry. Signals of UV photons through the
fine structure lines are considered to be stronger at locations of more
abundant chemical species of C I, C II and O I. Such environments would be
realized where strong fluxes of non-ionizing UV line photons available for the
pumping up of fine structure levels exist, and simultaneously ionizing UV
photons are effectively shielded by dense H I regions. Signals from H I regions
of moderately large densities induced by redshifted UV photons emitted at the
point sources are found to be dominantly large over those of others. We discuss
the detectability of the signals, and show that signals from idealized
environments will be possibly detected by radio observations with
next-generation arrays to come after the Atacama Large Millimeter/submillimeter
Array (ALMA).Comment: 23 pages, 21 figures, significant revisions in Secs. 2, 3, and 4, and
Appendix, main conclusions unchanged, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Multi-threshold second-order phase transition
We present a theory of the multi-threshold second-order phase transition, and
experimentally demonstrate the multi-threshold second-order phase transition
phenomenon. With carefully selected parameters, in an external cavity diode
laser system, we observe second-order phase transition with multiple (three or
four) thresholds in the measured power-current-temperature three dimensional
phase diagram. Such controlled death and revival of second-order phase
transition sheds new insight into the nature of ubiquitous second-order phase
transition. Our theory and experiment show that the single threshold
second-order phase transition is only a special case of the more general
multi-threshold second-order phase transition, which is an even richer
phenomenon.Comment: 5 pages, 3 figure
The role of oversight in foreign-national only prisons: counteracting the disapplication of rehabilitation
In several European countries, prisons have been created solely to house foreign national prisoners without leave to remain. Contrary to contemporary international human rights law and standards on prison management, there seems to be a trend towards the disapplication of rehabilitative theory and practice for this group of prisoners. In particular, they do not seem to receive the same preparation for release and reintegrative support as other prisoners. This paper explores the role international standards and oversight bodies have in upholding rehabilitation as the foundational objective for prison management in foreign national only prisons. It outlines the changes to the prison estate, policy and regime that have resulted from the increasing focus on removal within both the prison and penal process. The consequences of the disapplication of rehabilitation for prisons, prison officers, prisoners and society itself are analysed before the paper moves to examine the role oversight bodies could and should play in the protection of the rights of this vulnerable category of prisoner and the primacy that should be accorded to rehabilitative theory and practice. It concludes by asking whether such standards and oversight have inverted the panopticon by placing the trigger for international reactions in the hands of prisoners and NGOs
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A multilevel neo-institutional analysis of infection prevention and control in English hospitals: coerced safety culture change?
Despite committed policy, regulative and professional efforts on healthcare safety, little is known about how such macro-interventions permeate organisations and shape culture over time. Informed by neo-institutional theory, we examined how inter-organisational influences shaped safety practices and inter-subjective meanings following efforts for coerced culture change. We traced macro-influences from 2000 to 2015 in infection prevention and control (IPC). Safety perceptions and meanings were inductively analysed from 130 in-depth qualitative interviews with senior- and middle-level managers from 30 English hospitals. A total of 869 institutional interventions were identified; 69% had a regulative component. In this context of forced implementation of safety practices, staff experienced inherent tensions concerning the scope of safety, their ability to be open and prioritisation of external mandates over local need. These tensions stemmed from conflicts among three co-existing institutional logics prevalent in the NHS. In response to requests for change, staff flexibly drew from a repertoire of cognitive, material and symbolic resources within and outside their organisations. They crafted 'strategies of action', guided by a situated assessment of first-hand practice experiences complementing collective evaluations of interventions such as 'pragmatic', 'sensible' and also 'legitimate'. Macro-institutional forces exerted influence either directly on individuals or indirectly by enriching the organisational cultural repertoire
DHODH modulates transcriptional elongation in the neural crest and melanoma
Melanoma is a tumour of transformed melanocytes, which are originally derived from the embryonic neural crest. It is unknown to what extent the programs that regulate neural crest development interact with mutations in the BRAF oncogene, which is the most commonly mutated gene in human melanoma1. We have used zebrafish embryos to identify the initiating transcriptional events that occur on activation of human BRAF(V600E) (which encodes an amino acid substitution mutant of BRAF) in the neural crest lineage. Zebrafish embryos that are transgenic for mitfa:BRAF(V600E) and lack p53 (also known as tp53) have a gene signature that is enriched for markers of multipotent neural crest cells, and neural crest progenitors from these embryos fail to terminally differentiate. To determine whether these early transcriptional events are important for melanoma pathogenesis, we performed a chemical genetic screen to identify small-molecule suppressors of the neural crest lineage, which were then tested for their effects on melanoma. One class of compound, inhibitors of dihydroorotate dehydrogenase (DHODH), for example leflunomide, led to an almost complete abrogation of neural crest development in zebrafish and to a reduction in the self-renewal of mammalian neural crest stem cells. Leflunomide exerts these effects by inhibiting the transcriptional elongation of genes that are required for neural crest development and melanoma growth. When used alone or in combination with a specific inhibitor of the BRAF(V600E) oncogene, DHODH inhibition led to a marked decrease in melanoma growth both in vitro and in mouse xenograft studies. Taken together, these studies highlight developmental pathways in neural crest cells that have a direct bearing on melanoma formation
Tune in to your emotions: a robust personalized affective music player
The emotional power of music is exploited in a personalized affective music player (AMP) that selects music for mood enhancement. A biosignal approach is used to measure listeners’ personal emotional reactions to their own music as input for affective user models. Regression and kernel density estimation are applied to model the physiological changes the music elicits. Using these models, personalized music selections based on an affective goal state can be made. The AMP was validated in real-world trials over the course of several weeks. Results show that our models can cope with noisy situations and handle large inter-individual differences in the music domain. The AMP augments music listening where its techniques enable automated affect guidance. Our approach provides valuable insights for affective computing and user modeling, for which the AMP is a suitable carrier application
Observations of Arp 220 using Herschel-SPIRE: An Unprecedented View of the Molecular Gas in an Extreme Star Formation Environment
We present Herschel SPIRE-FTS observations of Arp~220, a nearby ULIRG. The
FTS continuously covers 190 -- 670 microns, providing a good measurement of the
continuum and detection of several molecular and atomic species. We detect
luminous CO (J = 4-3 to 13-12) and water ladders with comparable total
luminosity; very high-J HCN absorption; OH+, H2O+, and HF in absorption; and CI
and NII. Modeling of the continuum yields warm dust, with T = 66 K, and an
unusually large optical depth of ~5 at 100 microns. Non-LTE modeling of the CO
shows two temperature components: cold molecular gas at T ~ 50 K and warm
molecular gas at T ~1350 K. The mass of the warm gas is 10% of the cold gas,
but dominates the luminosity of the CO ladder. The temperature of the warm gas
is in excellent agreement with H2 rotational lines. At 1350 K, H2 dominates the
cooling (~20 L_sun/M_sun) in the ISM compared to CO (~0.4 L_sun/M_sun). We
found that only a non-ionizing source such as the mechanical energy from
supernovae and stellar winds can excite the warm gas and satisfy the energy
budget of ~20 L_sun/M_sun. We detect a massive molecular outflow in Arp 220
from the analysis of strong P-Cygni line profiles observed in OH+, H2O+, and
H2O. The outflow has a mass > 10^{7} M_sun and is bound to the nuclei with
velocity < 250 km/s. The large column densities observed for these molecular
ions strongly favor the existence of an X-ray luminous AGN (10^{44} ergs/s) in
Arp 220.Comment: Accepted in ApJ on September 1, 201
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