Low temperature thermoluminescence of GAGG:Ce and LuAG:Pr scintillator crystals has been studied by means of the Tmax–Tstop method. It is shown that the glow curves of both materials are ...superpositions of discrete glow peaks and broad bands due to quasi-continuous Gaussian distributions of trapping levels. A model function has been built and trap parameters have been evaluated.
•Thermoluminescence of GAGG:Ce and LuAG:Pr has been studied by the Tmax–Tstop method.•Glow curves have been analyzed in order to derive trap parameters.•Inclusion of quasi-continuous trap distributions has resulted in high quality fits.
Luminescent properties of HfO2:Ti ceramics were investigated in the 16–300 K range of temperatures. A red shift of a broad emission band from about 490 nm at room temperature to 520 nm at 16 K was ...observed. The room temperature emission was showed to consist of two overlapping bands. The shorter wavelength band intensity was strongly reduced below about 80 K. The variation of the emission peak position correlates with the variation of decay time of the luminescence which increases by a factor of about 250, between room temperature (6 μs) and 25 K (1.7 ms). In the 25–300 K temperature range the decay traces were practically monoexponential while below 25 K two clearly different components were observed with time constants of about 300–700 μs and ∼3–4.4 ms. What is more, with decrease of temperature from 25 to 16 K the shorter decay time component dominates the longer one. Nevertheless, an average decay time calculated for emissions below 25 K was still 1.65–1.7 ms. The analysis of experimental data suggests that the emitting center is, most likely, a four level system with the two lowest levels separated by about 734 cm–1. The lower of these two levels is clearly a triplet as transitions starting from it are strongly forbidden. The higher, presumably a singlet, is thermally populated at temperatures above 80 K, contributing to the spectra (shorter wavelengths emission) and decays (shorter effective decay times). The experimental data were also analyzed in a frame of a simple model and a good agreement between an experiment and theory was achieved. A configuration coordinate diagram is also presented, showing the levels due to the Ti ion in 3+ and 4+ charge states taking part in the charge transfer (CT) excitation and emission processes.
β-Ga2O3 is an emerging ultra-wide bandgap (4.9 eV) oxide semiconductor that additionally scintillates under gamma excitation. A unique combination of transparency in the UV/visible spectrum, ...semiconducting, and scintillation properties makes that compound interesting for fundamental studies of underlying physics and design of novel devices, in particular compact detectors for gamma radiation. Undoped, and singly (Ce, Si, Al), doubly (Ce + Si, Ce + Al), and triply (Ce + Al + Si) doped bulk β-Ga2O3 single crystals were grown by the Czochralski method under very similar conditions and systematically studied in terms of electrical and optical properties that were correlated with scintillation light yield under gamma excitation. A wide spectrum of doping enabled to control the free electron concentration in semiconducting β-Ga2O3 crystals within almost three orders of magnitude (7 × 1015–6 × 1018 cm−3) with the Hall mobility approaching 150 cm2 V−1s−1. The maximum of light yield under gamma excitation was recorded for undoped and Ce-doped β-Ga2O3 single crystals having the free electron concentration of mid 1016 cm−3. The light yield significantly decreases for both electrically insulating and highly conducting (Si-doped) crystals. None of the dopants (Ce, Si, Al) introduces any absorption bands in the spectral region of light emission (340–410 nm) under gamma excitation. The dopants in quest do not affect the structure of neither cathodoluminescence (CL) nor radioluminescence (RL) emissions, but modify their absolute intensity. A double-band structure of RL spectra corresponds to UV and blue emissions observed in CL spectra that are assigned to self-trapped excitons.
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•Doped semiconducting β-Ga2O3 was grown and studied for gamma radiation detection.•The crystals are fully transparent to scintillation emissions at 340–410 nm.•Maximum of light yield was found at free electron concentration of mid 1016 cm−3.•Luminescence spectra point to self-trapped excitons in scintillation mechanism.
Bovine respiratory disease complex (BRDC) is an infectious disease of cattle that is caused by a combination of viral and/or bacterial pathogens. Selection for cattle with reduced susceptibility to ...respiratory disease would provide a permanent tool for reducing the prevalence of BRDC. The objective of this study was to identify BRDC susceptibility loci in pre-weaned Holstein calves as a prerequisite to using genetic improvement as a tool for decreasing the prevalence of BRDC. High density SNP genotyping with the Illumina BovineHD BeadChip was conducted on 1257 male and 757 female Holstein calves from California (CA), and 767 calves identified as female from New Mexico (NM). Of these, 1382 were classified as BRDC cases, and 1396 were classified as controls, with all phenotypes assigned using the McGuirk health scoring system. During the acquisition of blood for DNA isolation, two deep pharyngeal and one mid-nasal diagnostic swab were obtained from each calf for the identification of bacterial and viral pathogens. Genome-wide association analyses were conducted using four analytical approaches (EIGENSTRAT, EMMAX-GRM, GBLUP and FvR). The most strongly associated SNPs from each individual analysis were ranked and evaluated for concordance. The heritability of susceptibility to BRDC in pre-weaned Holstein calves was estimated.
The four statistical approaches produced highly concordant results for 373 top ranked SNPs that defined 126 chromosomal regions for the CA population. Similarly, in NM, 370 SNPs defined 138 genomic regions that were identified by all four approaches. When the two populations were combined (i.e., CA + NM) and analyzed, 324 SNPs defined 116 genomic regions that were associated with BRDC across all analytical methods. Heritability estimates for BRDC were 21% for both CA and NM as individual populations, but declined to 13% when the populations were combined.
Four analytical approaches utilizing both single and multi-marker association methods revealed common genomic regions associated with BRDC susceptibility that can be further characterized and used for genomic selection. Moderate heritability estimates were observed for BRDC susceptibility in pre-weaned Holstein calves, thereby supporting the application of genomic selection to reduce the prevalence of BRDC in U.S. Holsteins.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Haldane’s rule (HR, impairment of fertility and/or viability of interracial hybrids) seems to be one of few generalizations in evolutionary biology. The validity of HR has been confirmed in ...animals, and more recently in some dioecious plants (
Silene
and
Rumex
). Dioecious
Rumex hastatulus
has two races differing in the sex chromosome system: Texas (T) and North Carolina (NC), and T × NC males showed both reduced pollen fertility and rarity—two classical symptoms of Haldane’s rule (HR). The reduced fertility of these plants has a simple mechanistic explanation, but the reason for their rarity was not elucidated. Here, we measured selected physiological parameters related to the antioxidant defense system in parental races and reciprocal hybrids of
R. hastatulus
. We showed that the X-autosome configurations, as well as asymmetries associated with Y chromosomes and cytoplasm, could modulate this system in hybrids. The levels and quantitative patterns of the measured parameters distinguish the T × NC hybrid from the other analyzed forms. Our observations suggest that the rarity of T × NC males is caused postzygotically and most likely related to the higher level of oxidative stress induced by the chromosomal incompatibilities. It is the first report on the physiological aspects of HR in plants.
Yersinia pestis, the causative agent of plague, is one of the most virulent microorganisms known. The outer membrane protein X (OmpX) in Y. pestis KIM is required for efficient bacterial adherence to ...and internalization by cultured HEp-2 cells and confers resistance to human serum. Here, we tested the contribution of OmpX to disease progression in the fully virulent Y. pestis CO92 strain by engineering a deletion mutant and comparing its ability in mediating pneumonic plague to that of the wild type in two animal models. The deletion of OmpX delayed the time to death up to 48 h in a mouse model and completely attenuated virulence in a rat model of disease. All rats challenged with 1 x 10⁸ CFU of the ompX mutant survived, compared to the 50% lethal dose (LD₅₀) of 1.2 x 10³ CFU for the wild-type strain. Because murine serum is not bactericidal for the ompX mutant, the mechanism underlying the delay in time to death in mice was attributed to loss of adhesion/internalization properties but not serum resistance. The rat model, which is most similar to humans, highlighted the critical role of serum resistance in disease. To resolve conflicting evidence for the role of Y. pestis lipopolysaccharide (LPS) and OmpX in serum resistance, ompX was cloned into Escherichia coli D21 and three isogenic derivatives engineered to have progressively truncated LPS core saccharides. OmpX-mediated serum resistance, adhesiveness, and invasiveness, although dependent on LPS core length, displayed these functions in E. coli, independently of other Yersinia proteins and/or LPS. Also, autoaggregation was required for efficient OmpX-mediated adhesiveness and internalization but not serum resistance.
•A new method was developed to compare multi-drug resistance plasmid invasion into E. coli biofilms.•Invasibility varied greatly among plasmids.•Longer donor-to-biofilm exposure time and better donor ...attachment enhanced invasibility, but not biofilm age.
In spite of the contribution of plasmids to the spread of antibiotic resistance in human pathogens, little is known about the transferability of various drug resistance plasmids in bacterial biofilms. The goal of this study was to compare the efficiency of transfer of 19 multidrug resistance plasmids into Escherichia coli recipient biofilms and determine the effects of biofilm age, biofilm-donor exposure time, and donor-to-biofilm attachment on this process. An E. coli recipient biofilm was exposed separately to 19 E. coli donors, each with a different plasmid, and transconjugants were determined by plate counting. With few exceptions, plasmids that transferred well in a liquid environment also showed the highest transferability in biofilms. The difference in transfer frequency between the most and least transferable plasmid was almost a million-fold. The ‘invasibility’ of the biofilm by plasmids, or the proportion of biofilm cells that acquired plasmids within a few hours, depended not only on the type of plasmid, but also on the time of biofilm exposure to the donor and on the ability of the plasmid donor to attach to the biofilm, yet not on biofilm age. The efficiency of donor strain attachment to the biofilm was not affected by the presence of plasmids. The most invasive plasmid was pHH2-227, which based on genome sequence analysis is a hybrid between IncU-like and IncW plasmids. The wide range in transferability in an E. coli biofilm among plasmids needs to be taken into account in our fight against the spread of drug resistance.
Measurements of pulse height spectra and scintillation time profiles performed on Czochralski-grown β-Ga2O3, β-Ga2O3:Ce, and β-Ga2O3:Ce,Si crystals are reported. The highest value of scintillation ...yield, 7040 ph/MeV, was achieved for pure β-Ga2O3 at a low free electron concentration, nevertheless Ce-doped crystals could also approach high values thereof. Si-codoping, however, decreases the scintillation yield. The presence of Ce, and the more of Ce and Si, in β-Ga2O3 significantly increases the contribution of the fastest components in scintillation time profiles, which makes β-Ga2O3 a very fast scintillator under γ-excitation.
A high-quality bulk single crystal of β-Ga2O3 has been grown by the Czochralski method and its basic scintillation characteristics (light yield, energy resolution, proportionality, and scintillation ...decay times) have been investigated. All the samples cut from the crystal show promising scintillation yields between 8400 and 8920 ph/MeV, which is a noticeable step forward compared to previous studies. The remaining parameters, i.e. the energy resolution slightly above 10% (at 662 keV) and the scintillation mean decay time just under 1 μs, are at the same level as we have formerly recognized for β-Ga2O3. The proportionality of yield seems not to deviate from standards determined by other commercial scintillators.
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