1,184 research outputs found
Radio-Frequency Spectroscopy of Ultracold Fermions
Radio-frequency techniques were used to study ultracold fermions. We observed
the absence of mean-field "clock" shifts, the dominant source of systematic
error in current atomic clocks based on bosonic atoms. This is a direct
consequence of fermionic antisymmetry. Resonance shifts proportional to
interaction strengths were observed in a three-level system. However, in the
strongly interacting regime, these shifts became very small, reflecting the
quantum unitarity limit and many-body effects. This insight into an interacting
Fermi gas is relevant for the quest to observe superfluidity in this system.Comment: 6 pages, 6 figure
Dust, Ice and Gas in Time (DIGIT) Herschel program first results: A full PACS-SED scan of the gas line emission in protostar DK Cha
DK Cha is an intermediate-mass star in transition from an embedded
configuration to a star plus disk stage. We aim to study the composition and
energetics of the circumstellar material during this pivotal stage. Using the
Range Scan mode of PACS on the Herschel Space Observatory, we obtained a
spectrum of DK Cha from 55 to 210 micron as part of the DIGIT Key Program.
Almost 50 molecular and atomic lines were detected, many more than the 7 lines
detected in ISO-LWS. Nearly the entire ladder of CO from J=14-13 to 38-37
(E_u/k = 4080 K), water from levels as excited as E_u/k = 843 K, and OH lines
up to E_u/k = 290 K were detected. The continuum emission in our PACS SED scan
matches the flux expected from a model consisting of a star, a surrounding disk
of 0.03 Solar mass, and an envelope of a similar mass, supporting the
suggestion that the object is emerging from its main accretion stage.
Molecular, atomic, and ionic emission lines in the far-infrared reveal the
outflow's influence on the envelope. The inferred hot gas can be photon-heated,
but some emission could be due to C-shocks in the walls of the outflow cavity.Comment: 4 Page letter, To appear in A&A special issue on Hersche
Herschel observations of the hydroxyl radical (OH) in young stellar objects
Water in Star-forming regions with Herschel (WISH) is a Herschel Key Program
investigating the water chemistry in young stellar objects (YSOs) during
protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical
network most closely linked to the formation and destruction of H2O.
High-temperature chemistry connects OH and H2O through the OH + H2 H2O + H
reactions. Formation of H2O from OH is efficient in the high-temperature regime
found in shocks and the innermost part of protostellar envelopes. Moreover, in
the presence of UV photons, OH can be produced from the photo-dissociation of
H2O. High-resolution spectroscopy of the OH 163.12 micron triplet towards HH 46
and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far
Infrared (HIFI) on board Herschel. The low- and intermediate-mass YSOs HH 46,
TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were
observed with the Photodetector Array Camera and Spectrometer (PACS) in four
transitions of OH and two [OI] lines. The OH transitions at 79, 84, 119, and
163 micron and [OI] emission at 63 and 145 micron were detected with PACS
towards the class I low-mass YSOs as well as the intermediate-mass and class I
Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333
IRAS 2A, though the 119 micron was detected in absorption. With HIFI, the
163.12 micron was not detected from HH 46 and only tentatively detected from
NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46
constrains the line width (FWHM > 11 km/s) and indicates that the OH emission
likely originates from shocked gas. This scenario is supported by trends of the
OH flux increasing with the [OI] flux and the bolometric luminosity. Similar OH
line ratios for most sources suggest that OH has comparable excitation
temperatures despite the different physical properties of the sources.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel
special issue
Reduction of the size of datasets by using evolutionary feature selection: the case of noise in a modern city
Smart city initiatives have emerged to mitigate the negative effects of a very fast growth of urban areas. Most of the population in our cities are exposed to high levels of noise that generate discomfort and different health problems. These issues may be mitigated by applying different smart cities solutions, some of them require high accurate noise information to provide the best quality of serve possible. In this study, we have designed a machine learning approach based on genetic algorithms to analyze noise data captured in the university campus. This method reduces the amount of data required to classify the noise by addressing a feature selection optimization problem. The experimental results have shown that our approach improved the accuracy in 20% (achieving an accuracy of 87% with a reduction of up to 85% on the original dataset).Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech.
This research has been partially funded by the Spanish MINECO and FEDER projects TIN2016-81766-REDT (http://cirti.es), and TIN2017-88213-R (http://6city.lcc.uma.es)
Microscopic Dynamics in a Strongly Interacting Bose-Einstein Condensate
An initially stable 85Rb Bose-Einstein condensate (BEC) was subjected to a
carefully controlled magnetic field pulse in the vicinity of a Feshbach
resonance. This pulse probed the strongly interacting regime for the
condensate, with calculated values for the diluteness parameter (na^3) ranging
from 0.01 to 0.5. The field pulse was observed to cause loss of atoms from the
condensate on remarkably short time scales (>=10 microsec). The dependence of
this loss on magnetic field pulse shape and amplitude was measured. For
triangular pulses shorter than 1 ms, decreasing the pulse length actually
increased the loss, until extremely short time scales (a few tens of
microseconds) were reached. Such time scales and dependencies are very
different from those expected in traditional condensate inelastic loss
processes, suggesting the presence of new microscopic BEC physics.Comment: 4 pages in latex2E, 4 eps figures; revised Fig.1, revised
scatt.lengths, added discussion, new refs., resubmitted to PR
Association between Ambient Noise Exposure and School Performance of Children Living in An Urban Area: A Cross-Sectional Population-Based Study
16 pages Article disponible Ă l'adresse suivante : http://link.springer.com/article/10.1007%2Fs11524-013-9843-6International audienceMost of the studies investigating the effects of the external noise on children's school performance have concerned pupils in schools exposed to high levels due to aircraft or freeway traffic noise. However, little is known about the consequences of the chronic ambient noise exposure at a level commonly encountered in residential urban areas. This study aimed to assess the relationship between the school performance of 8- to 9-year-old-children living in an urban environment and their chronic ambient noise exposure at home and at school. The children's school performances on the national standardized assessment test in French and mathematics were compared with the environmental noise levels. Children's exposure to ambient noise was calculated in front of their bedrooms (Lden) and schools (LAeq,day) using noise prediction modeling. Questionnaires were distributed to the families to collect potential confounding factors. Among the 746 respondent children, 586 were included in multilevel analyses. On average, the LAeq,day at school was 51.5Â dB (SD=â4.5 dB; rangeâ=â38-58Â dB) and the outdoor Lden at home was 56.4Â dB (SD=â4.4 dB; rangeâ=â44-69Â dB). LAeq,day at school was associated with impaired mathematics score (pâ=â0.02) or impaired French score (pâ=â0.01). For aâ+â10Â dB gap, the French and mathematics scores were on average lower by about 5.5 points. Lden at home was significantly associated with impaired French performance when considered alone (pâ<â10(-3)) and was borderline significant when the combined home-school exposure was considered (pâ=â0.06). The magnitude of the observed effect on school performance may appear modest, but should be considered in light of the number of people who are potentially chronically exposed to similar environmental noise levels
Uncertainty-principle noise in vacuum-tunneling transducers
The fundamental sources of noise in a vacuum-tunneling probe used as an
electromechanical transducer to monitor the location of a test mass are
examined using a first-quantization formalism. We show that a tunneling
transducer enforces the Heisenberg uncertainty principle for the position and
momentum of a test mass monitored by the transducer through the presence of two
sources of noise: the shot noise of the tunneling current and the momentum
fluctuations transferred by the tunneling electrons to the test mass. We
analyze a number of cases including symmetric and asymmetric rectangular
potential barriers and a barrier in which there is a constant electric field.
Practical configurations for reaching the quantum limit in measurements of the
position of macroscopic bodies with such a class of transducers are studied
Gene transfer into hepatocytes using asialoglycoprotein receptor mediated endocytosis of DNA complexed with an artificial tetra-antennary galactose ligand
We have constructed an artificial ligand for the hepatocyte-specific asialoglycoprotein receptor for the purpose of generating a synthetic delivery system for DNA. This ligand has a tetra-antennary structure, containing four terminal galactose residues on a branched carrier peptide. The carbohydrate residues of this glycopeptide were introduced by reductive coupling of lactose to the alpha- and epsilon-amino groups of the two N-terminal lysines on the carrier peptide. The C-terminus of the peptide, containing a cysteine separated from the branched N-terminus by a 10 amino acid spacer sequence, was used for conjugation to 3-(2-pyridyldithio)propionate-modified polylysine via disulfide bond formation. Complexes containing plasmid DNA bound to these galactose-polylysine conjugates have been used for asialoglycoprotein receptor-mediated transfer of a luciferase gene into human (HepG2) and murine (BNL CL.2) hepatocyte cell lines. Gene transfer was strongly promoted when amphipathic peptides with pH-controlled membrane-disruption activity, derived from the N-terminal sequence of influenza virus hemagglutinin HA-2, were also present in these DNA complexes. Thus, we have essentially borrowed the small functional domains of two large proteins, asialoglycoprotein and hemagglutinin, and assembled them into a supramolecular complex to generate an efficient gene-transfer system
Quantum interference structures in the conductance plateaus of gold nanojunctions
The conductance of breaking metallic nanojunctions shows plateaus alternated
with sudden jumps, corresponding to the stretching of stable atomic
configurations and atomic rearrangements, respectively. We investigate the
structure of the conductance plateaus both by measuring the voltage dependence
of the plateaus' slope on individual junctions and by a detailed statistical
analysis on a large amount of contacts. Though the atomic discreteness of the
junction plays a fundamental role in the evolution of the conductance, we find
that the fine structure of the conductance plateaus is determined by quantum
interference phenomenon to a great extent.Comment: 4 pages, 4 figure
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