334 research outputs found
Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow-Townes limit
A comprehensive investigation of the frequency-noise spectral density of a
free-running mid-infrared quantum-cascade laser is presented for the first
time. It provides direct evidence of the leveling of this noise down to a white
noise plateau, corresponding to an intrinsic linewidth of a few hundred Hz. The
experiment is in agreement with the most recent theory on the fundamental
mechanism of line broadening in quantum-cascade lasers, which provides a new
insight into the Schawlow-Townes formula and predicts a narrowing beyond the
limit set by the radiative lifetime of the upper level.Comment: 4 pages, 4 figure
Peripheral venous blood gases and pulse-oximetry in acute cardiogenic pulmonary oedema
Background: The role of venous blood gases as an alternative to arterial blood gases in patients with severe acute heart failure has not been established. Objective: To assess the correlation between arterial and peripheral venous blood gases together with pulse-oximetry (SpO2), as well as to estimate arterial values from venous samples in the first hours upon admission of patients with acute cardiogenic pulmonary oedema. Methods: Simultaneous venous and arterial blood samples were extracted on admission and over the next 1, 2, 3, 4, and 10 hours. SpO2 was also registered at the same intervals. Results: A total of 178 pairs of samples were obtained from 34 consecutive patients with acute cardiogenic pulmonary oedema. Arterial and venous blood gases followed a parallel course in the first hours, showing high correlation rates at all time intervals. Venous samples underestimated pH (mean difference â0.028) and overestimated CO2 (+5.1 mmHg) and bicarbonate (+1 mEq/l). Conversely, SpO2 tended to underestimate SaO2 (mean±SD: 93.1±9.1 vs. 94.2±8.4). Applying simple mathematical formulae based on these differences, arterial values were empirically calculated from venous samples, showing acceptable agreement in the BlandâAltman test. Likewise, a venous pH 51.3 mmHg, and bicarbonate <22.8 mEq/l could fairly identify arterial acidosis, either respiratory or metabolic, with a test accuracy of 92, 68, and 91%, respectively. Conclusions: In patients with cardiogenic pulmonary oedema, arterial blood gas disturbances may be estimated from peripheral venous samples. By monitoring SpO2 simultaneously, arterial punctures could often be avoide
Symbionts do not affect the mating incompatibility between the Brazilian-1 and Peruvian morphotypes of the Anastrepha fraterculus cryptic species complex
The South American fruit fly, Anastrepha fraterculus, is clearly undergoing a speciation process. Among others, two of their morphotypes, the Brazilian-1 and Peruvian, have accumulated differences in pre- and post-zygotic mechanisms resulting in a degree of reproductive isolation. Both harbor a different strain of Wolbachia, which is a widespread endosymbiotic bacterium among many invertebrates producing a range of reproductive effects. In this paper, we studied the role of this bacterium as one of the factors involved in such isolation process. Infected and cured laboratory colonies were used to test pre- and post-zygotic effects, with special emphasis in uni- and bi-directional cytoplasmic incompatibility (CI). We showed that Wolbachia is the only known reproductive symbiont present in these morphotypes. Wolbachia reduced the ability for embryonic development in crosses involving cured females and infected males within each morphotype (uni-directional CI). This inhibition showed to be more effective in the Peruvian morphotype. Bi-directional CI was not evidenced, suggesting the presence of compatible Wolbachia strains. We conclude that Wolbachia is not directly involved in the speciation process of these morphotypes. Other mechanisms rather than CI should be explored in order to explain the reduced mating compatibility between the Brazilian-1 and Peruvian morphotypes.Instituto de BiotecnologĂaFil: Devescovi, Francisco. Instituto Nacional de TecnologĂa Agropecuaria (INTA). Instituto de AgrobiotecnologĂa y BiologĂa Molecular; Argentina. Instituto Nacional de TecnologĂa Agropecuaria (INTA). Instituto de GenĂ©tica. Laboratorio de GenĂ©tica de Insectos de Importancia EconĂłmica; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Conte, Claudia Alejandra. Instituto Nacional de TecnologĂa Agropecuaria (INTA). Instituto de GenĂ©tica. Laboratorio de GenĂ©tica de Insectos de Importancia EconĂłmica; ArgentinaFil: Augustinos, Antonios A. Vienna International Centre. Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. Insect Pest Control Laboratory; AustriaFil: Cancio Martinez, Elena I. Vienna International Centre. Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. Insect Pest Control Laboratory; AustriaFil: Segura, Diego Fernando. Instituto Nacional de TecnologĂa Agropecuaria (INTA). Instituto de AgrobiotecnologĂa y BiologĂa Molecular; Argentina. Instituto Nacional de TecnologĂa Agropecuaria (INTA). Instituto de GenĂ©tica. Laboratorio de GenĂ©tica de Insectos de Importancia EconĂłmica; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Caceres, Carlos. Vienna International Centre. Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. Insect Pest Control Laboratory; AustriaFil: Lanzavecchia, Silvia Beatriz. Instituto Nacional de TecnologĂa Agropecuaria (INTA). Instituto de GenĂ©tica "Ewald A. Favret"; ArgentinaFil: Bourtzis, Kostas. Vienna International Centre. Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. Insect Pest Control Laboratory; Austri
A Laser System for the Spectroscopy of Highly-Charged Bismuth Ions
We present and characterize a laser system for the spectroscopy on
highly-charged ^209Bi^82+ ions at a wavelength of 243.87 nm. For absolute
frequency stabilization, the laser system is locked to a near-infra-red laser
stabilized to a rubidium transition line using a transfer cavity based locking
scheme. Tuning of the output frequency with high precision is achieved via a
tunable rf offset lock. A sample-and-hold technique gives an extended tuning
range of several THz in the UV. This scheme is universally applicable to the
stabilization of laser systems at wavelengths not directly accessible to atomic
or molecular resonances. We determine the frequency accuracy of the laser
system using Doppler-free absorption spectroscopy of Te_2 vapour at 488 nm.
Scaled to the target wavelength of 244 nm, we achieve a frequency uncertainty
of \sigma_{244nm} = 6.14 MHz (one standard deviation) over six days of
operation.Comment: Contribution to the special issue on "Trapped Ions" in "Applied
Physics B
Discovery of non-nucleoside inhibitors of HIV-1 reverse transcriptase competing with the nucleotide substrate
How odd! A new class of non-nucleoside reverse transcriptase inhibitors with a 6-vinylpyrimidine scaffold (1) has been found to inhibit HIV-1 reverse transcriptase (RT) by competition with the nucleotide substrate after binding to the non-nucleoside inhibitor binding pocket of the enzyme. Molecular modeling studies have been performed to elucidate their peculiar behavior
A Marine Biodiversity Observation Network for Genetic Monitoring of Hard-Bottom Communities (ARMS-MBON)
Marine hard-bottom communities are undergoing severe change under the influence of multiple drivers, notably climate change, extraction of natural resources, pollution and eutrophication, habitat degradation, and invasive species. Monitoring marine biodiversity in such habitats is, however, challenging as it typically involves expensive, non-standardized, and often destructive sampling methods that limit its scalability. Differences in monitoring approaches furthermore hinders inter-comparison among monitoring programs. Here, we announce a Marine Biodiversity Observation Network (MBON) consisting of Autonomous Reef Monitoring Structures (ARMS) with the aim to assess the status and changes in benthic fauna with genomic-based methods, notably DNA metabarcoding, in combination with image-based identifications. This article presents the results of a 30-month pilot phase in which we established an operational and geographically expansive ARMS-MBON. The network currently consists of 20 observatories distributed across European coastal waters and the polar regions, in which 134 ARMS have been deployed to date. Sampling takes place annually, either as short-term deployments during the summer or as long-term deployments starting in spring. The pilot phase was used to establish a common set of standards for field sampling, genetic analysis, data management, and legal compliance, which are presented here. We also tested the potential of ARMS for combining genetic and image-based identification methods in comparative studies of benthic diversity, as well as for detecting non-indigenous species. Results show that ARMS are suitable for monitoring hard-bottom environments as they provide genetic data that can be continuously enriched, re-analyzed, and integrated with conventional data to document benthic community composition and detect non-indigenous species. Finally, we provide guidelines to expand the network and present a sustainability plan as part of the European Marine Biological Resource Centre (www.embrc.eu)
Global hybrids from the semiclassical atom theory satisfying the local density linear response
We propose global hybrid approximations of the exchange-correlation (XC)
energy functional which reproduce well the modified fourth-order gradient
expansion of the exchange energy in the semiclassical limit of many-electron
neutral atoms and recover the full local density approximation (LDA) linear
response. These XC functionals represent the hybrid versions of the APBE
functional [Phys. Rev. Lett. 106, 186406, (2011)] yet employing an additional
correlation functional which uses the localization concept of the correlation
energy density to improve the compatibility with the Hartree-Fock exchange as
well as the coupling-constant-resolved XC potential energy. Broad energetical
and structural testings, including thermochemistry and geometry, transition
metal complexes, non-covalent interactions, gold clusters and small
gold-molecule interfaces, as well as an analysis of the hybrid parameters, show
that our construction is quite robust. In particular, our testing shows that
the resulting hybrid, including 20\% of Hartree-Fock exchange and named hAPBE,
performs remarkably well for a broad palette of systems and properties, being
generally better than popular hybrids (PBE0 and B3LYP). Semi-empirical
dispersion corrections are also provided.Comment: 12 pages, 4 figure
Cold and trapped metastable noble gases
We review experimental and theoretical work on cold, trapped metastable noble
gases. We em- phasize the aspects which distinguish work with these atoms from
the large body of work on cold, trapped atoms in general. These aspects include
detection techniques and collision processes unique to metastable atoms. We
describe several experiments exploiting these unique features in fields
including atom optics and statistical physics. We also discuss precision
measurements on these atoms including fine structure splittings, isotope
shifts, and atomic lifetimes
Calibration of the Logarithmic-Periodic Dipole Antenna (LPDA) Radio Stations at the Pierre Auger Observatory using an Octocopter
An in-situ calibration of a logarithmic periodic dipole antenna with a
frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of
a radio station system used for detection of cosmic ray induced air showers at
the Engineering Radio Array of the Pierre Auger Observatory, the so-called
Auger Engineering Radio Array (AERA). The directional and frequency
characteristics of the broadband antenna are investigated using a remotely
piloted aircraft (RPA) carrying a small transmitting antenna. The antenna
sensitivity is described by the vector effective length relating the measured
voltage with the electric-field components perpendicular to the incoming signal
direction. The horizontal and meridional components are determined with an
overall uncertainty of 7.4^{+0.9}_{-0.3} % and 10.3^{+2.8}_{-1.7} %
respectively. The measurement is used to correct a simulated response of the
frequency and directional response of the antenna. In addition, the influence
of the ground conductivity and permittivity on the antenna response is
simulated. Both have a negligible influence given the ground conditions
measured at the detector site. The overall uncertainties of the vector
effective length components result in an uncertainty of 8.8^{+2.1}_{-1.3} % in
the square root of the energy fluence for incoming signal directions with
zenith angles smaller than 60{\deg}.Comment: Published version. Updated online abstract only. Manuscript is
unchanged with respect to v2. 39 pages, 15 figures, 2 table
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