1,792 research outputs found
Signatures of Dark Matter Scattering Inelastically Off Nuclei
Direct dark matter detection focuses on elastic scattering of dark matter
particles off nuclei. In this study, we explore inelastic scattering where the
nucleus is excited to a low-lying state of 10-100 keV, with subsequent prompt
de-excitation. We calculate the inelastic structure factors for the odd-mass
xenon isotopes based on state-of-the-art large-scale shell-model calculations
with chiral effective field theory WIMP-nucleon currents. For these cases, we
find that the inelastic channel is comparable to or can dominate the elastic
channel for momentum transfers around 150 MeV. We calculate the inelastic
recoil spectra in the standard halo model, compare these to the elastic case,
and discuss the expected signatures in a xenon detector, along with
implications for existing and future experiments. The combined information from
elastic and inelastic scattering will allow to determine the dominant
interaction channel within one experiment. In addition, the two channels probe
different regions of the dark matter velocity distribution and can provide
insight into the dark halo structure. The allowed recoil energy domain and the
recoil energy at which the integrated inelastic rates start to dominate the
elastic channel depend on the mass of the dark matter particle, thus providing
a potential handle to constrain its mass.Comment: 9 pages, 7 figures. Matches resubmitted version to Phys. Rev. D. One
figure added; supplemental material (fits to the structure functions) added
as an Appendi
Goethite Dissolution in the Presence of Phytosiderophores: Rates, Mechanisms, and the Synergistic Effect of Oxalate
The purpose of this study was the elucidation of the chemical mechanism of an important process in iron acquisition by graminaceous plants: the dissolution of iron oxides in the presence of phytosiderophores. We were particularly interested in the effects of diurnal root exudation of phytosiderophores and of the presence of other organic ligands in the rhizosphere of graminaceous plants on the dissolution mechanism. Phytosiderophores of the type 2′-deoxymugineic acid (DMA) were purified from the root exudates of wheat plants (Triticum aestivum L. cv. Tamaro). DMA-promoted dissolution of goethite under steady-state and non-steady-state conditions and its dependence on pH, adsorbed DMA concentration, and the presence of the organic ligand oxalate were studied. We show that dissolution of goethite by phytosiderophores follows a surface controlled ligand promoted dissolution mechanism. We also found that oxalate, an organic ligand commonly found in rhizosphere soils, has a synergistic effect on the steady-state dissolution of goethite by DMA. Under non-steady-state addition of the phytosiderophore, mimicking the diurnal exudation pattern of phytosiderophore release, a fast dissolution of iron is triggered in the presence of oxalate. To investigate the efficiency of these mechanisms in plant iron acquisition, wheat plants were grown on a substrate amended with goethite as only iron source. The chlorophyll status of these plants was similar to iron-fertilized plants and significantly higher than in plants grown in iron free nutrient solutions. This demonstrates that wheat can efficiently mobilize iron, even from well crystalline goethite that is usually considered unavailable for plant nutritio
The sources of sex differences in aging in annual fishes
Intersexual differences in life span (age at death) and aging (increase in mortality risk associated with functional deterioration) are widespread among animals, from nematodes to humans. Males often live shorter than females, but there is substantial unexplained variation among species and populations. Despite extensive research, it is poorly understood how life span differences between the sexes are modulated by an interplay among genetic, environmental and social factors. The goal of our study was to test how sex differences in life span and ageing are modulated by social and environmental factors, and by intrinsic differences between males and females. To disentangle the complex basis of sex differences in life span and aging, we combined comparative data from sex ratios in 367 natural populations of four species of African annual killifish with experimental results on sex differences in life span and aging from eight laboratory populations tested in treatments that varied social and environmental conditions. In the wild, females consistently outlived males. In captivity, sex-specific mortality depended on social conditions. In social-housed experimental groups, male-biased mortality persisted in two aggressive species, but ceased in two placid species. When social and physical contacts were prevented by housing all fish individually, male-biased mortality ceased in all four species. This outcome held across benign and challenging environmental conditions. Fitting demographic survival models revealed that increased baseline mortality was primarily responsible for a shorter male life span in social-housing conditions. The timing and rate of aging were not different between the sexes. No marker of functional aging we recorded in our study (lipofuscin accumulation, proliferative changes in kidney and liver) differed between males and females, despite their previously confirmed association with functional aging in Nothobranchius killifish. We show that sex differences in life span and aging in killifish are driven by a combination of social and environmental conditions, rather than differential functional aging. They are primarily linked to sexual selection but precipitated through multiple processes (predation, social interference). This demonstrates how sex-specific mortality varies among species even within an ecologically and evolutionary discrete lineage and explains how external factors mediate this difference
Kinesin's force generation mechanism : study and practical application
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 72-80).Chimeric kinesin 1 (KHC) / kinesin 5 (Eg5) constructs were used to study the force generation mechanism of the motor protein. The kinesin family of proteins walk along microtubules to carry cargo or pull microtubules along each other and do so by hydrolyzing a single ATP per 8nm step. The mechanism that is employed by kinesin to generate the force necessary for motion is not completely understood. One recent model, the cover neck bundle (CNB) model, utilizes two structural elements of the motor (the coverstrand, which is at the N-terminus of the motorhead) and [beta]9, which is part of the necklinker (C-terminus of the motorhead) to form a beta sheet. The CNB folds toward the motor head and causes the rear, unbound head to travel from behind to in front of the bound motorhead. Recent investigations have shown that the CNB produces enough force to explain single molecule experiments, and that when the CNB is not allowed to form by deletion of the coverstrand, the motor looses the ability to generate force. Recent experiments on dimeric forms of Eg5 (a member of the kinesin 5 family) have shown that the motor is capable of generating nearly analogous amounts of force as kinesin 1, but that it generally dissociates from the microtubule under load rather than coming to a true stall. To investigate the applicability of the CNB model of force generation and to see if a motor with high force capabilities could be generated, these chimeras employed the Eg5 CNB (and in some cases L13), and the rest of the kinesin 1 motorhead. It was found from experiments with a stationary optical trap to measure stall force and the force-velocity relationship of the motors as well as unloaded measurements, such as processivity and velocity, that motors with a matched CNB operated the best, however the use of the Eg5 CNB did not reproduce the force generation capabilities of dimeric Eg5 constructs. These results suggest that perhaps while the CNB mechanism is very important to force generation, it may not be the full explanation. A possible link between the CNB's effect on the rate of the mechanical step of the mechanochemical cycle and the stall force is discussed. This link between mechanical rate and stall force is a potential avenue for rational design of kinesin motors for a specific stall force. Secondly, these results show that the parts of kinesin are not directly interchangeable, and that careful consideration of the interactions between parts must be considered when engineering these motors. A second set of experiments were designed to explore whether the CNB mechanism could be exploited for a rational purpose. The literature consists of many reports of various methods to target kinesin and stop its motility for therapeutic reason. For example, some chemotherapies target kinesin to treat cancer. In this way, an antibody was designed to bind specifically with the coverstrand, thus hopefully disrupting the CNB formation and mechanism of force generation. These experiments demonstrated the the antibody was successful in targeting the coverstrand and in inhibiting kinesin's motion.by William R. Hesse.S.M
Continuum and Emission-Line Properties of Broad Absorption Line Quasars
We investigate the continuum and emission-line properties of 224 broad
absorption line quasars (BALQSOs) with 0.9<z<4.4 drawn from the Sloan Digital
Sky Survey (SDSS) Early Data Release (EDR), which contains 3814 bona fide
quasars. We find that low-ionization BALQSOs (LoBALs) are significantly
reddened as compared to normal quasars, in agreement with previous work.
High-ionization BALQSOs (HiBALs) are also more reddened than the average
nonBALQSO. Assuming SMC-like dust reddening at the quasar redshift, the amount
of reddening needed to explain HiBALs is E(B-V)~0.023 and LoBALs is
E(B-V)~0.077 (compared to the ensemble average of the entire quasar sample). We
find that there are differences in the emission-line properties between the
average HiBAL, LoBAL, and nonBAL quasar. These differences, along with
differences in the absorption line troughs, may be related to intrinsic quasar
properties such as the slope of the intrinsic (unreddened) continuum; more
extreme absorption properties are correlated with bluer intrinsic continua.
Despite the differences among BALQSO sub-types and nonBALQSOs, BALQSOs appear
to be drawn from the same parent population as nonBALQSOs when both are
selected by their UV/optical properties. We find that the overall fraction of
traditionally defined BALQSOs, after correcting for color-dependent selection
effects due to different SEDs of BALQSO and nonBALQSOs, is 13.4+/-1.2% and
shows no significant redshift dependence for 1.7<z<3.45. After a rough
completeness correction for the effects of dust extinction, we find that
approximately one in every six quasars is a BALQSO.Comment: 35 pages, 11 figures (1 color), 1 table; accepted by A
The Intrinsic Fractions and Radio Properties of Low Ionization Broad Absorption Line Quasars
Low-ionization (MgII, FeII, FeIII) broad absorption line quasars (LoBALs)
probe a relatively obscured quasar population, and could be at an early
evolutionary stage for quasars. We study the intrinsic fractions of LoBALs
using the SDSS, 2MASS, and FIRST surveys. We find that the LoBAL fractions of
the near infra-red (NIR) and radio samples are approximately 5--7 times higher
than those measured in the optical sample. This suggests that the fractions
measured in the NIR and radio bands are closer to the intrinsic fractions of
the populations, and that the optical fractions are significantly biased due to
obscuration effects, similar to high-ionization broad absorption line quasars
(HiBALs). We also find that the LoBAL fractions decrease with increasing radio
luminosities, again, similar to HiBALs. In addition, we find tentative evidence
for high fractions of LoBALs at high NIR luminosities, especially for FeLoBALs
with a fraction of ~18 per cent at M_K_s < -31 mag. This population of NIR
luminous LoBALs may be at an early evolutionary stage of quasar evolution. We
use a two-component model of LoBALs including a pure geometric component and a
luminosity dependent component at high NIR luminosities, and obtain better fits
than those from a pure geometric model. Therefore, the LoBAL population can be
modelled as a hybrid of both the geometric and evolutionary models, where the
geometric component constitutes 3.4\pm0.3, 5.8\pm0.4, and 1.5\pm0.3 per cent of
the quasar population for BI-LoBALs, AI-LoBALs, and FeLoBALs, respectively.
Considering a population of obscured quasars that do not enter the SDSS survey,
which could have a much higher LoBAL fraction, we expect that intrinsic
fraction of LoBALs could be even higher.Comment: 10 pages, 6 figures, submitted to MNRA
Cytauxzoonosis in Indiana, USA: a case series of cats infected with Cytauxzoon felis (2018-2022)
CASE SERIES SUMMARY: This case series describes six cases involving seven cats naturally infected with Cytauxzoon felis in Indiana, USA. Medical records were retrospectively reviewed and all available information on signalment, history, clinical and diagnostic findings, treatment, outcome and pathology was reported. Cats infected with C felis were domestic shorthairs, were aged between 2 and 9 years and all but one of the cats were male. The seven infected cats originated from five counties in southwestern Indiana. Six of seven cats were found to have acute cytauxzoonosis based on clinical signs, gross pathologic lesions, observation of C felis in tissues and/or detection of C felis DNA. One cat was identified as a subclinical survivor cat with no known clinical history of cytauxzoonosis.
RELEVANCE AND NOVEL INFORMATION: The reported cases are the first confirmed reports of acute and chronic cytauxzoonosis in cats from Indiana and document an expansion in the range of C felis. Veterinary practitioners in Indiana should consider infection with C felis as a differential diagnosis for cats that present with fever, inappetence, lethargy, depression, dehydration, dyspnea, hemolytic crisis, anorexia or icterus. Administration of approved acaricides to cats currently offers the best protection and control against C felis infection
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