610 research outputs found
Modelling the role of chance in mating dynamics
This undergraduate honors thesis examines the role of chance in mating dynamics, focusing on the popular measures of Is and OSR and whether or not they are accurate measures of sexual selection. The first chapter is an overview of sexual selection and how biologists typically measure it, and the second chapter describes the modelling scenarios we created to assess the interaction of Is and OSR with both chance and parental investment. Our results show that Is and OSR have indeed been used incorrectly, and that we should shift our focus to trait-based methods when measuring sexual selection
Entanglement Patterns in Mutually Unbiased Basis Sets for N Prime-state Particles
A few simply-stated rules govern the entanglement patterns that can occur in
mutually unbiased basis sets (MUBs), and constrain the combinations of such
patterns that can coexist (ie, the stoichiometry) in full complements of p^N+1
MUBs. We consider Hilbert spaces of prime power dimension (as realized by
systems of N prime-state particles, or qupits), where full complements are
known to exist, and we assume only that MUBs are eigenbases of generalized
Pauli operators, without using a particular construction. The general rules
include the following: 1) In any MUB, a particular qupit appears either in a
pure state, or totally entangled, and 2) in any full MUB complement, each qupit
is pure in p+1 bases (not necessarily the same ones), and totally entangled in
the remaining p^N-p. It follows that the maximum number of product bases is
p+1, and when this number is realized, all remaining p^N-p bases in the
complement are characterized by the total entanglement of every qupit. This
"standard distribution" is inescapable for two qupits (of any p), where only
product and generalized Bell bases are admissible MUB types. This and the
following results generalize previous results for qubits and qutrits. With
three qupits there are three MUB types, and a number of combinations (p+2) are
possible in full complements. With N=4, there are 6 MUB types for p=2, but new
MUB types become possible with larger p, and these are essential to the
realization of full complements. With this example, we argue that new MUB
types, showing new entanglement characteristics, should enter with every step
in N, and when N is a prime plus 1, also at critical p values, p=N-1. Such MUBs
should play critical roles in filling complements.Comment: 27 pages, one figure, to be submitted to Physical Revie
On fault-tolerance with noisy and slow measurements
It is not so well-known that measurement-free quantum error correction
protocols can be designed to achieve fault-tolerant quantum computing. Despite
the potential advantages of using such protocols in terms of the relaxation of
accuracy, speed and addressing requirements on the measurement process, they
have usually been overlooked because they are expected to yield a very bad
threshold as compared to error correction protocols which use measurements.
Here we show that this is not the case. We design fault-tolerant circuits for
the 9 qubit Bacon-Shor code and find a threshold for gates and preparation of
(30% of the best known result for the
same code using measurement based error correction) while admitting up to 1/3
error rates for measurements and allocating no constraints on measurement
speed. We further show that demanding gate error rates sufficiently below the
threshold one can improve the preparation threshold to .
We also show how these techniques can be adapted to other
Calderbank-Shor-Steane codes.Comment: 11 pages, 7 figures. v3 has an extended exposition and several
simplifications that provide for an improved threshold value and resource
overhea
Assessment of Five Chilling Tolerance Traits and GWAS Mapping in Rice Using the USDA Mini-Core Collection
Rice (Oryza sativa L.) is often exposed to cool temperatures during spring planting in temperate climates. A better understanding of genetic pathways regulating chilling tolerance will enable breeders to develop varieties with improved tolerance during germination and young seedling stages. To dissect chilling tolerance, five assays were developed; one assay for the germination stage, one assay for the germination and seedling stage, and three for the seedling stage. Based on these assays, five chilling tolerance indices were calculated and assessed using 202 O. sativa accessions from the Rice Mini-Core (RMC) collection. Significant differences between RMC accessions made the five indices suitable for genome-wide association study (GWAS) based quantitative trait loci (QTL) mapping. For young seedling stage indices, japonica and indica subspecies clustered into chilling tolerant and chilling sensitive accessions, respectively, while both subspecies had similar low temperature germinability distributions. Indica subspecies were shown to have chilling acclimation potential. GWAS mapping uncovered 48 QTL at 39 chromosome regions distributed across all 12 rice chromosomes. Interestingly, there was no overlap between the germination and seedling stage QTL. Also, 18 QTL and 32 QTL were in regions discovered in previously reported bi-parental and GWAS based QTL mapping studies, respectively. Two novel low temperature seedling survivability (LTSS)–QTL, qLTSS3-4 and qLTSS4-1, were not in a previously reported QTL region. QTL with strong effect alleles identified in this study will be useful for marker assisted breeding efforts to improve chilling tolerance in rice cultivars and enhance gene discovery for chilling tolerance
Tight-binding study of interface states in semiconductor heterojunctions
Localized interface states in abrupt semiconductor heterojunctions are
studied within a tight-binding model. The intention is to provide a microscopic
foundation for the results of similar studies which were based upon the
two-band model within the envelope function approximation. In a two-dimensional
description, the tight-binding Hamiltonian is constructed such that the
Dirac-like bulk spectrum of the two-band model is recovered in the continuum
limit. Localized states in heterojunctions are shown to occur under conditions
equivalent to those of the two-band model. In particular, shallow interface
states are identified in non-inverted junctions with intersecting bulk
dispersion curves. As a specific example, the GaSb-AlSb heterojunction is
considered. The matching conditions of the envelope function approximation are
analyzed within the tight-binding description.Comment: RevTeX, 11 pages, 3 figures, to appear in Phys. Rev.
Correction: The Complete Sequence of the Acacia ligulata Chloroplast Genome Reveals a Highly Divergent clpP1 Gene
The authors would like to amend this article based on the discovery that the originally published Acacia ligulata sequence contains assembly errors, which came to light after the publication of the article
Pharmacology of DB844, an orally active aza analogue of pafuramidine, in a monkey model of second stage human African trypanosomiasis
Novel drugs to treat human African trypanosomiasis (HAT) are still urgently needed despite the recent addition of nifurtimox-eflornithine combination therapy (NECT) to WHO Model Lists of Essential Medicines against second stage HAT, where parasites have invaded the central nervous system (CNS). The pharmacology of a potential orally available lead compound, N-methoxy-6-{5-[4-(N-methoxyamidino) phenyl]-furan-2-yl}-nicotinamidine (DB844), was evaluated in a vervet monkey model of second stage HAT, following promising results in mice. DB844 was administered orally to vervet monkeys, beginning 28 days post infection (DPI) with Trypanosoma brucei rhodesiense KETRI 2537. DB844 was absorbed and converted to the active metabolite 6-[5-(4-phenylamidinophenyl)-furanyl-2-yl]-nicotinamide (DB820), exhibiting plasma C(max) values of 430 and 190 nM for DB844 and DB820, respectively, after the 14th dose at 6 mg/kg qd. A 100-fold reduction in blood trypanosome counts was observed within 24 h of the third dose and, at the end of treatment evaluation performed four days post the last drug dose, trypanosomes were not detected in the blood or cerebrospinal fluid of any monkey. However, some animals relapsed during the 300 days of post treatment monitoring, resulting in a cure rate of 3/8 (37.5%) and 3/7 (42.9%) for the 5 mg/kg×10 days and the 6 mg/kg×14 days dose regimens respectively. These DB844 efficacy data were an improvement compared with pentamidine and pafuramidine both of which were previously shown to be non-curative in this model of CNS stage HAT. These data show that synthesis of novel diamidines with improved activity against CNS-stage HAT was possible
CdZnTe strip detectors as sub-millimeter resolution imaging gamma radiation spectrometers
We report γ-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for γ-ray measurements in the range of 20-600 keV. The prototype is a 1.5 mm thick, 64×64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8×8 stripe region of the prototype we measured good spectroscopic uniformity and sub-pitch (~0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals. We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results with the data. The data indicate that cathode signal-as well as the anode signal-arises more strongly from the conduction electrons rather than the holes
Accurate six-band nearest-neighbor tight-binding model for the pi-bands of bulk graphene and graphene nanoribbons
Accurate modeling of the pi-bands of armchair graphene nanoribbons (AGNRs)
requires correctly reproducing asymmetries in the bulk graphene bands as well
as providing a realistic model for hydrogen passivation of the edge atoms. The
commonly used single-pz orbital approach fails on both these counts. To
overcome these failures we introduce a nearest-neighbor, three orbital per atom
p/d tight-binding model for graphene. The parameters of the model are fit to
first-principles density-functional theory (DFT) - based calculations as well
as to those based on the many-body Green's function and screened-exchange (GW)
formalism, giving excellent agreement with the ab initio AGNR bands. We employ
this model to calculate the current-voltage characteristics of an AGNR MOSFET
and the conductance of rough-edge AGNRs, finding significant differences versus
the single-pz model. These results show that an accurate bandstructure model is
essential for predicting the performance of graphene-based nanodevices.Comment: 5 figure
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