bluuebunny/crossref_metadata_2025 huggingface dataset:
Flavor, temperature and magnetic field dependence of the QCD phase diagram: magnetic catalysis and its inverse
Authors: Ahmad Aftab , Bashir Adnan , Bedolla Marco A , Cobos-Martínez J J
Published: January 2021

We study dynamical chiral symmetry breaking for quarks in the fundamental representation of SU(N
c) for the N
f number of light quark flavors. We also investigate the phase diagram of quantum chromodynamics at finite temperature T and/or in the presence of a constant external magnetic field eB. The unified formalism for this analysis is provided by a symmetry-preserving Schwinger–Dyson equation treatment of a vector × vector contact interaction model which encodes several well-established features of quantum chromodynamics to mimic the latter as closely as possible. Deconfinement and chiral symmetry restoration are triggered above a critical value of N
f at T = 0 = eB. On the other hand, increasing temperature itself screens strong interactions, thus ensuring that a smaller value of N
f is sufficient to restore chiral symmetry at higher temperatures. We also observe the well-known phenomenon of magnetic catalysis for a strong enough magnetic field. However, we note that if the effective coupling strength of the model decreases as a function of magnetic field, it can trigger inverse magnetic catalysis in a certain window of this functional dependence. Our model allows for the simultaneous onset of dynamical chiral symmetry breaking and confinement for each case. Qualitative as well as quantitative predictions of our simple but effective model are in reasonably satisfactory agreement with lattice results and other reliable and refined predictions based upon intricate continuum studies of quantum chromodynamics.
Impact of noble-gas filler atoms on the lattice thermal conductivity of CoSb3 skutterudites: first-principles modelling
Authors: Tang Jianqin , Skelton Jonathan M
Published: January 2021

We present a systematic first-principles modelling study of the structural dynamics and thermal transport in CoSb3 skutterudites with a series of noble-gas filler atoms. Filling with chemically-inert atoms provides an idealised model for isolating the effects of the fillers from the impact of redox changes to the host electronic structure. A range of analysis techniques are proposed to estimate the filler rattling frequencies, to quantify the separate impacts of the fillers on the phonon group velocities and lifetimes, and to show how changes to the phonon spectra and interaction strengths lead to suppressed lifetimes. The noble-gas fillers are found to reduce the thermal conductivity of the CoSb3 framework by up to 15% primarily by suppressing the group velocities of low-lying optic modes. The filler rattling frequencies are determined by a detailed balance of increasing atomic mass and stronger interactions with the framework, and are found to be a good predictor of the impact on the heat transport. Lowering the rattling frequency below ∼1.5 THz by selecting heavy fillers that interact weakly with the framework is predicted to lead to a much larger suppression of the thermal transport, by inducing avoided crossings in the acoustic-mode dispersion and facilitating enhanced scattering and a consequent large reduction in phonon lifetimes. Approximate rattling frequencies determined from the harmonic force constants may therefore provide a useful metric for selecting filler atoms to optimise the thermal transport in skutterudites and other cage compounds such as clathrates.
Development of skeletal systems for ICRP pediatric mesh-type reference computational phantoms
Authors: Choi Chansoo , Shin Bangho , Yeom Yeon Soo , Han Haegin , Ha Sangseok , Moon Sungho , Son Gahee , Nguyen Thang Tat , Kim Chan Hyeong , Chung Beom Sun , Bolch Wesley E
Published: January 2021

In 2016, the International Commission on Radiological Protection (ICRP) launched Task Group 103 (TG 103) for the explicit purpose of developing a new generation of adult and pediatric reference computational phantoms, named ‘mesh-type reference computational phantoms (MRCPs)’, that can overcome the limitations of voxel-type reference computational phantoms (VRCPs) of ICRP Publications 110 and 143 due to their finite voxel resolutions and the nature of voxel geometry. After completing the development of the adult MRCPs, TG 103 has started the development of pediatric MRCPs comprising 10 phantoms (male and female versions of the reference newborn, 1-year-old, 5-year-old, 10-year-old, and 15-year-old). As part of the TG 103 project, within the present study, the skeletal systems, one of the most important and complex organ systems of the body, were developed for each phantom age and sex. The developed skeletal systems, while closely preserving the original bone topology of the pediatric VRCPs, present substantial improvements in the anatomy of complex and/or small bones. In order to investigate the dosimetric impact of the developed skeletons, the average absorbed doses and the specific absorbed fractions for radiosensitive skeletal tissues (i.e. active marrow and bone endosteum) were computed for some selected external and internal exposure cases, which were then compared with those calculated with the skeletons of pediatric VRCPs. The comparison result showed that the dose values of the pediatric MRCPs were generally similar to those of the pediatric VRCPs for highly penetrating radiations (e.g. photons >200 keV); however, for weakly penetrating radiations (e.g. photons ⩽200 keV and electrons), significant differences up to a factor of 140 were observed.
High-precision time delay estimation of narrowband radio signal by PHAT-LSTM
Authors: Yao Shunyu , Meng Qiao , Chen Congyan , Tariq Irfan , Zhou Chenye , Liu Wei
Published: January 2021

In this article, a novel method for high-precision time-delay estimation (TDE) of narrow-band signals is proposed. It is based on a cross-correlation function, phase spectrum, long short-term memory (LSTM) artificial neural network to unwrap the phase transform (PHAT) spectrum of the cross-correlation function. The PHAT-LSTM architecture consists of three parts. The first part is a wrapping parameter estimator (WPE) used to estimate the wrapping parameter of the base-band phase spectrum. The second part, a wrapping classifier (WCF), is a single output network used to compensate the drawbacks of the WPE. The third part, a synthesize and fine estimator, synthesizes the information from the WPE and WCF to unwrap the phase and estimate the delay according to the phase-delay model. The input of the PHAT-LSTM are fast Fourier transforms of snapshot data from two receiving channels. In addition, the dimension of the input signals was dramatically decreased compared with other deep learning-based TDE methods. Simulation results show that the root mean square error (RMSE) of the PHAT-LSTM is decreased in low signal-to-noise ratio (SNR) compared with traditional TDE methods. When the SNR = 10 dB or 0 dB, the RMSE of TDE was about ten times smaller than that of traditional methods.
Laser shock pressing of silver nanowires on flexible substrates to fabricate highly uniform transparent conductive electrode films
Authors: Noh Jihun , Kim Dongsik
Published: January 2021

Large surface roughness, wire-to-wire junction resistance, and poor adhesion strength of percolated silver nanowire films on polymer substrates are critical issues responsible for low shunt resistance, electron concentration, and thermal damage, resulting in the occurrence of dark spots and damage to flexible electronic devices. Therefore, the fabrication of transparent conductive electrode (TCE) thin films with high surface smoothness and enhanced film properties without the aforementioned problems is essential. Herein, we propose an innovative method to mechanically join silver nanowires on heat-sensitive polymer substrates using a laser-induced shock pressure wave generated by laser ablation of a sacrificial layer. The physical joining mechanism and film properties, that is, sheet resistance, transmittance, adhesion strength, and flexibility, were experimentally analyzed. When a high laser shock pressure was applied to the silver nanowires, plastic deformation occurred; thus, a sintered network film was fabricated through solid-state atomic diffusion at the nanowire junctions. Under optimal process conditions, the sintered films showed high resistance to the adhesion tape test (R/R0 = 1.15), a significantly reduced surface roughness less than 6 nm, and comparable electrical conductivity (8 ± 2Ω·sq−1) and visible transmittance (84% ± 3%) to typical joining methods. Consequently, this work demonstrates that the laser-induced shock pressing technique has strong potential for the production of TCE metal films on heat-sensitive flexible substrates with film properties superior to those of films produced by conventional methods.
Flexible capacitive sensor based on 2D-titanium dioxide nanosheets/bacterial cellulose composite film
Authors: Sriphan Saichon , Charoonsuk Thitirat , Khaisaat Supharada , Sawanakarn Oubonwan , Pharino Utchawadee , Phunpruch Saranya , Maluangnont Tosapol , Vittayakorn Naratip
Published: January 2021

In this paper, titanium dioxide nanosheets (Ti0.91O2 NSs) were incorporated into bacterial cellulose (BC) film for dielectric property tuning while maintaining the flexibility of the resulting composite paper. By taking advantage of the improved dielectric constant, the nanosheets/BC composites were employed as capacitive sensors. The fabricated devices showed the highest sensing performance of ∼2.44 × 10−3 kPa−1 from 0 to 30 N when incorporating as little as 3 vol% of Ti0.91O2 NSs (or ∼2 wt% Ti). Stable operation and high robustness of the sensor were demonstrated, where simple human motions could be efficiently monitored. This study provided a route for preparing flexible and low-cost BC composite paper for capacitive sensor. The strategy for enhancing the dielectric properties as well as sensing performances of the BC demonstrated herein will be essential for the future development of biocompatible, low-cost, and eco-friendly wearable electronics.
One-step synthesis of blue–green luminescent carbon dots by a low-temperature rapid method and their high-performance antibacterial effect and bacterial imaging
Authors: Zhao Dan , Zhang Rui , Liu Xuemei , Huang Xianju , Xiao Xincai , Yuan Lin
Published: January 2021

Due to the global infection problem caused by the abuse of antibiotics, the preparation of novel antibacterial nanomaterials is a key and basic requirement for applications in antibacterial and bacterial imaging fields. This paper reports the one-step preparation of blue–green-emitting carbon dots (CDs) under low temperature (80 °C) with glucose as the carbon source, citric acid as the dehydrating agent, and polyethyleneimine as the nitrogen source. Through inhibition zone tests and minimum inhibitory concentration (MIC) experiments, the inhibitory abilities of prepared CDs against various microorganisms, including gram-positive bacteria, gram-negative bacteria and fungi, were compared. It is worth mentioning that the MIC of CDs against Staphylococcus aureus reaches 4.7 μg ml−1, and the CDs exhibit excellent biocompatibility. Moreover, studies on visual-treatment therapy, in which infection treatment can be performed at the same time as bacterial imaging, with the prepared functional antibacterial CDs based on fluorescence confocal imaging would be beneficial to their promising future in medical and biological fields.
Conceptual understanding procedure to elicit metacognition with pre-service physics teachers
Authors: Carpendale Jared , Cooper Rebecca
Published: January 2021

Contemporary views on physics education in high schools promote the need for students to develop their conceptual understanding about physics phenomena. However, teaching in this way requires specialized professional knowledge and for pre-service physics teachers, such knowledge needs to be scaffolded and developed. A strategy to support this knowledge development includes eliciting metacognition, where pre-service teachers have opportunities to explore and reconstruct their own knowledge, views, and attitudes about teaching physics. The conceptual understanding procedure (CUP) was developed in the late 1990s at Monash University, initially to support physics students in their first year at university. In particular, a CUP was used to support these students’ understanding of mechanics and highlight their potential alternate conceptions. Researchers found that two thirds of the students involved in this procedure reported that it had positive effects on their understanding and their ideas were clarified. In this paper, we investigate our own use of CUPs as physics teacher educators as a strategy to elicit metacognition with pre-service physics teachers to support their professional knowledge development. Our pre-service physics teachers act as high school physics students to complete the task, and then as physics teachers to explore the pedagogical purposes of the CUP. Ultimately, this process of working in these two roles, while reflecting on their immediate experiences, elicits metacognition in a meaningful way that scaffolds and supports the development of the specialized knowledge required for effective teaching. Thus, we recommend a CUP is a suitable and worthwhile pedagogical strategy to use when supporting pre-service physics teachers’ to elicit metacognition and support professional knowledge development to promote teaching for conceptual understanding.
The invisibility of time dilation
Authors: Hughes Theo , Kersting Magdalena
Published: January 2021

Recently, the physics education community has taken a keen interest in modernising physics education. However, while topics in modern physics have great potential to engage students, these topics are abstract and hard-to-visualise. Therefore, many students hold mistaken pictures and misconceptions, which can impede learning. In this article, we expose a pervasive misconception about relativistic time dilation by presenting a thought experiment illustrating the difference between visual observation and coordinate measurement. We also point out how existing language can mislead and confuse students. In response, we describe an instructional approach that introduces world-maps, world-pictures and event-diagrams to clarify the applicability of key equations in special relativity for improved understanding. By unpacking ‘the invisibility of time dilation’ from the perspectives of both physics and pedagogy, we aim to help teachers provide clearer instruction.
Feedback–feedforward control for high-speed trajectory tracking of an amplified piezoelectric actuator
Authors: Saleem Ashraf , Mesbah Mostefa , Shafiq Muhammad
Published: January 2021

Piezoelectric actuators (PAs) are increasingly used in industrial and research applications requiring high speed and accurate positioning at the micro and nano scales such as atomic force microscopy. This is due to their high positioning resolution, compactness, and fast response. There are, however, two main factors that significantly limit their performance, namely hysteresis and the structural resonance. To overcome these limitations, while avoiding using inversion-based feedforward compensators, we propose, a new learning controller for high speed amplified PA (APA) trajectory tracking. To further enhance the robustness of the APA against sensor noise and other disturbances, a simple proportional and integral (PI) controller is added in the feedback loop. The proposed feedback–feedforward controller compensates for the above-mentioned phenomena without requiring access to the ‘complex’ mathematical model of the APA. Using the notions of system passivity and finite gain stability, we show that the closed-loop system is stable, and the tracking error is bounded for continuous reference inputs. These results are experimentally confirmed using a sinusoidal reference input with varying frequencies. The controller is able to track reference signals with frequencies up to 500 Hz (very close to the resonance frequency of the APA) with relatively small tracking errors. To further assess the quality of the proposed controller, we compare its tracking performance against a previously proposed controller. We show that our controller consistently achieves smaller tracking errors and the performance gap between the two controllers increases with an increase in frequency. We finally show the advantage of using the feedforward learning controller by comparing the tracking performance of our feedforward–feedback controller against that of the PI. The results show a clear performance improvement and that this improvement becomes even more evident at higher frequencies.
Defects and dopants in zinc-blende aluminum arsenide: a first-principles study
Authors: Cao Jiangming , Huang Menglin , Liu Dingrong , Cai Zenghua , Wu Yu-Ning , Ye Xiang , Chen Shiyou
Published: January 2021

AlAs is a semiconductor that can form heterostructure, superlattice, and ternary alloy with GaAs. We systematically investigate the formation energies, transition energy levels, as well as defect and carrier densities of intrinsic defects and extrinsic impurities in AlAs using first-principles simulations. Most of the intrinsic defects, including vacancies, antisites and interstitials, show similar features as those of GaAs. Intrinsic defects are found not to be the origin of the n-type or p-type conductivity due to their high formation energies. For extrinsic dopants (Si, C, Mg and Cu), Mg can be an effective p-type dopant under both As-rich and As-poor conditions. Si-doping can introduce either n-type or p-type, depending on the specific growth condition. C serves as a p-type dopant under As-poor and As-moderate conditions, and Cu-doping has little effect on the conductivity.
Disentanglement approach to quantum spin ground states: field theory and stochastic simulation
Authors: De Nicola Stefano
Published: January 2021

While several tools have been developed to study the ground state of many-body quantum spin systems, the limitations of existing techniques call for the exploration of new approaches. In this manuscript we develop an alternative analytical and numerical framework for many-body quantum spin ground states, based on the disentanglement formalism. In this approach, observables are exactly expressed as Gaussian-weighted functional integrals over scalar fields. We identify the leading contribution to these integrals, given by the saddle point of a suitable effective action. Analytically, we develop a field-theoretical expansion of the functional integrals, performed by means of appropriate Feynman rules. The expansion can be truncated to a desired order to obtain analytical approximations to observables. Numerically, we show that the disentanglement approach can be used to compute ground state expectation values from classical stochastic processes. While the associated fluctuations grow exponentially with imaginary time and the system size, this growth can be mitigated by means of an importance sampling scheme based on knowledge of the saddle point configuration. We illustrate the advantages and limitations of our methods by considering the quantum Ising model in 1, 2 and 3 spatial dimensions. Our analytical and numerical approaches are applicable to a broad class of systems, bridging concepts from quantum lattice models, continuum field theory, and classical stochastic processes.
SubtypeDrug: a software package for prioritization of candidate cancer subtype-specific drugs
Authors: Han Xudong , Kong Qingfei , Liu Chonghui , Cheng Liang , Han Junwei
Published: January 2021

Cancer can be classified into various subtypes by its molecular, histological or clinical characteristics. Discovering cancer-subtype-specific drugs is a crucial step in personalized medicine. SubtypeDrug is a system biology R-based software package that enables the prioritization of subtype-specific drugs based on cancer expression data from samples of many subtypes. This provides a novel approach to identify the subtype-specific drug by considering biological functions regulated by drugs at the subpathway level. The operation modes include extraction of subpathways from biological pathways, identification of dysregulated subpathways induced by each drug, inference of sample-specific subpathway activity profiles, evaluation of drug-disease reverse association at the subpathways level, identification of cancer-subtype-specific drugs through subtype sample set enrichment analysis, and visualization of the results. Its capabilities enable SubtypeDrug to find subtype-specific drugs, which will fill the gaps in the recent tools which only identify the drugs for a particular cancer type. SubtypeDrug may help to facilitate the development of tailored treatment for patients with cancer. 

Availability and implementation

The package is implemented in R and available under GPL-2 license from the CRAN website (https://CRAN.R-project.org/package=SubtypeDrug).

Supplementary information

Supplementary data are available at Bioinformatics online.
A rarefaction-based extension of the LDM for testing presence–absence associations in the microbiome
Authors: Hu Yi-Juan , Lane Andrea , Satten Glen A
Published: January 2021

Motivation

Many methods for testing association between the microbiome and covariates of interest (e.g. clinical outcomes, environmental factors) assume that these associations are driven by changes in the relative abundance of taxa. However, these associations may also result from changes in which taxa are present and which are absent. Analyses of such presence–absence associations face a unique challenge: confounding by library size (total sample read count), which occurs when library size is associated with covariates in the analysis. It is known that rarefaction (subsampling to a common library size) controls this bias, but at the potential cost of information loss as well as the introduction of a stochastic component into the analysis. Currently, there is a need for robust and efficient methods for testing presence–absence associations in the presence of such confounding, both at the community level and at the individual-taxon level, that avoid the drawbacks of rarefaction.

Results

We have previously developed the linear decomposition model (LDM) that unifies the community-level and taxon-level tests into one framework. Here, we present an extension of the LDM for testing presence–absence associations. The extended LDM is a non-stochastic approach that repeatedly applies the LDM to all rarefied taxa count tables, averages the residual sum-of-squares (RSS) terms over the rarefaction replicates, and then forms an F-statistic based on these average RSS terms. We show that this approach compares favorably to averaging the F-statistic from R rarefaction replicates, which can only be calculated stochastically. The flexible nature of the LDM allows discrete or continuous traits or interactions to be tested while allowing confounding covariates to be adjusted for. Our simulations indicate that our proposed method is robust to any systematic differences in library size and has better power than alternative approaches. We illustrate our method using an analysis of data on inflammatory bowel disease (IBD) in which cases have systematically smaller library sizes than controls.

Availabilityand implementation

The R package LDM is available on GitHub at https://github.com/yijuanhu/LDM in formats appropriate for Macintosh or Windows.

Supplementary information

Supplementary data are available at Bioinformatics online.
Simulation of diffuse and stringy fibrosis in a bilayer interconnected cable model of the left atrium
Authors: Saliani Ariane , Irakoze Éric , Jacquemet Vincent
Published: January 2021

Aims

The aim of this study is to design a computer model of the left atrium for investigating fibre-orientation-dependent microstructure such as stringy fibrosis.

Methods and results

We developed an approach for automatic construction of bilayer interconnected cable models from left atrial geometry and epi- and endocardial fibre orientation. The model consisted of two layers (epi- and endocardium) of longitudinal and transverse cables intertwined-like fabric threads, with a spatial discretization of 100 µm. Model validation was performed by comparison with cubic volumetric models in normal conditions. Then, diffuse (n = 2904), stringy (n = 3600), and mixed fibrosis patterns (n = 6840) were randomly generated by uncoupling longitudinal and transverse connections in the interconnected cable model. Fibrosis density was varied from 0% to 40% and mean stringy obstacle length from 0.1 to 2 mm. Total activation time, apparent anisotropy ratio, and local activation time jitter were computed during normal rhythm in each pattern. Non-linear regression formulas were identified for expressing measured propagation parameters as a function of fibrosis density and obstacle length (stringy and mixed patterns). Longer obstacles (even below tissue space constant) were independently associated with prolonged activation times, increased anisotropy, and local fluctuations in activation times. This effect was increased by endo-epicardial dissociation and mitigated when fibrosis was limited to the epicardium.

Conclusion

Interconnected cable models enable the study of microstructure in organ-size models despite limitations in the description of transmural structures.
A qualitative study of VHA clinicians’ knowledge and perspectives on cannabis for medical purposes
Authors: Christensen Vivian A , Nugent Shannon M , Ayers Chelsea K , Morasco Benjamin J , Kansagara Devan
Published: January 2021

Background

The legalization of cannabis is expanding across the USA, and its use has increased significantly, including among Veterans. Although the Veterans Health Administration (VHA) abides by the classification of cannabis as a Schedule I substance, it recently recommended that clinicians discuss cannabis with their patients. Little is known about VHA clinicians’ perspectives on and knowledge of cannabis.

Objective

We sought to better understand clinicians’ attitudes, beliefs, knowledge and communication with patients regarding cannabis.

Methods

We conducted semi-structured phone interviews with 14 VHA clinicians. Interviews were audio-recorded, transcribed verbatim and analysed using qualitative thematic analysis.

Results

VA clinicians described ambivalence towards cannabis for therapeutic purposes and identified several factors that inhibit conversations about cannabis use with their patients including discomfort with the lack of product standardization; lack of research examining the effectiveness and risks of cannabis use; unfamiliarity with pharmacology, formulations, and dosing of cannabis; and uncertainty regarding VHA policy. Clinicians had differing views on cannabis in the context of the opioid crisis.

Conclusions

VA clinicians face challenges in navigating the topic of medical cannabis. Educational materials about cannabis products, dose and harms would be helpful to clinicians.
A GENETIC ANALYSIS OF TETRAHYMENA THAT HAVE ABORTED NORMAL DEVELOPMENT
Authors: Scholnick Steven B , Bruns Peter J
Published: January 2021

Conjugating Tetrahymena can abort the sexual cycle before the production of progeny somatic (macro-) nuclei and return to vegetative growth. We have analyzed the germinal (micronuclear) genotypes of these cells in order to determine the stage at which they aborted conjugation. Our data demonstrate that nearly all of these cells attempt meiosis, but that very few reach the successful completion of cross-fertilization. The resulting micronuclear genotypes suggest that either germinal chromosomes or entire nuclei are lost during an unsuccessful attempt at meiosis or cross-fertilization. We conclude that the decision to develop progeny macronuclei is made during meiosis and is dependent on the completion of some step necessary for successful cross-fertilization.
TWO CELL DIVISION CYCLE MUTANTS OF SACCHAROMYCES CEREVISIAE ARE DEFECTIVE IN TRANSMISSION OF MITOCHONDRIA TO ZYGOTES
Authors: Dutcher Susan K
Published: January 2021

Mutations in CDC genes of S. cerevisiae disrupt the cell cycle at specific stages. The experiments reported here demonstrate that two CDC genes, CDC5 and CDC27, are necessary for mitochondrial segregation as well as for nuclear division. The defect in the transmission of mitochondria was revealed by the examination of uninucleate and binucleate progeny of transient heterokaryons generated by using the kar1-1 mutation that disrupts nuclear fusion. One of the parents lacked mitochondrial DNA (?0) whereas the other parent had functional mitochondria (?+). When the parents of the heterokaryon were both wild-type (CDC), nearly all progeny received mitochondria at 21° and at 34°. Thirty-four of the 36 cdc mutations tested had no defect in transmission of mitochondria to zygotic progeny in crosses in which one parent was a cdc mutant and the other parent was not (CDC). However, the cdc5 and cdc27 mutations prevented the transmission of mitochondria to cdc progeny at 34° but not at 21°; CDC progeny received mitochondria at either temperature. This defect was observed in crosses of cdc5 or cdc27 by wild-type cells regardless of which parent donated mitochondria to the zygote. The defect in mitochondrial transmission cosegregated in meiotic tetrads with the defect in mitosis demonstrating that both are likely to be caused by the same temperature-sensitive mutation. These results indicate that the CDC5 and CDC27 gene products are essential in two motility-related processes: mitochondrial movement from the zygote to the progeny and in mitosis.—Furthermore, the results suggest that the function performed by the CDC5 and CDC27 gene products for mitochondrial transmission differ in some fundamental way from the function performed for mitosis. The function necessary for mitosis can be supplied to the cdc5 (or cdc27) nucleus by the CDC5 (or CDC27) nucleus in the same heterokaryon but the function necessary for mitochondrial transmission cannot. Perhaps the function needed for mitochondrial transmission must be performed in the cell cycle preceding the actual segregation of mitochondria whereas the function needed for nuclear segregation can be performed at the time that mitosis occurs.
DOSAGE COMPENSATION OF SERINE-4 TRANSFER RNA IN DROSOPHILA MELANOGASTER
Authors: Birchler James A , Owenby R Keith , Jacobson K Bruce
Published: January 2021

A dosage series of the X chromosome site for serine-4 transfer RNA consisting of one of three copies in females and one to two in males was constructed to test whether transfer RNA expression is governed by dosage compensation. A dosage effect on the level of the serine-4 isoacceptor was observed in both females and males when the structural locus was varied. However, in males, each dose had a relatively greater expression so the normal one dose was slightly greater than the total female value and the duplicated male had the highest relative expression of all the types examined. Serine-4 levels in males and females from an isogenic Oregon-R stock were similar. Thus the transfer RNA levels conform to the expectations of dosage compensation.
METHYL METHANESULFONATE MUTAGENESIS IN BACTERIOPHAGE T4
Authors: Drake John W
Published: January 2021

MMS induces diverse rII mutations from a wild-type background in bacteriophage T4. About 56% are base pair substitutions, about 30% are frameshift mutations, and the remainder is a miscellaneous set of rapidly reverting or leaky mutants of unknown composition; but deletions were not detected. MMS-induced forward mutation is sharply reduced by the mutations px and y, which also reduce ultraviolet, photodynamic and γ-ray mutagenesis and increase killing by all of these agents. Thus, many of the mutations arise via the T4 WXY system. The induction of G:C → A:T transitions was detected even in a px or y background using sensitive reversion tests, and the few forward rII mutations that were induced from this background also behaved like transition mutations. Thus, some MMS-induced mutations arise independently of the WXY system, perhaps as a result of the (rather weak) ability of MMS to alkylate the O6 position of guanine.
GENETIC PROPERTIES OF MUTATIONS AT THE PEP4 LOCUS IN SACCHAROMYCES CEREVISIAE
Authors: Zubenko George S , Park Frances J , Jones Elizabeth W
Published: January 2021

Yeast cells that inherit mutations at the PEP4 locus exhibit a pronounced phenotypic lag in the expression of the mutant phenotype imparted by these mutations. This lag appears to extend to all of the enzymes that are affected by the pep4-3 mutation. For at least two of the enzymatic activities, phenotypic lag shows mitotic cosegregation. Phenotypic lag is found for meiotic progeny and for mitotic segregants from heterokaryons. The phenotypic lag in the expression of the carboxypeptidase Y deficiency is abolished by nonsense mutations in either PRC1, the structural gene for carboxypeptidase Y, or PRB1, the structural gene for proteinase B. Models to explain these observations are proposed.
CHROMOSOME REARRANGEMENTS IN DICTYOSTELIUM DISCOIDEUM
Authors: Welker Dennis L , Metz Birgit A , Williams Keith L
Published: January 2021

A tandem duplication (D350(III,III)) of the whiB to radB interval of linkage group III has been characterized. The gene order on the duplication-bearing chromosome is: centromere, whiB500, radB+, whiB+, radB24, bsgA5, acrC4. Slow-growing, duplication-bearing strains (yellow-spored, radiation-resistant) produced four classes of faster growing sectors involving the whiB and radB loci: white-spored, radiation-sensitive (whiB500, radB24); white-spored, radiation-resistant (whiB500, radB+); yellow-spored, radiation-sensitive (whiB+, radB24); and yellow-spored, radiation-resistant. The first three classes can be explained as the products of single recombination events in which one copy of the whiB to radB interval was lost. The yellow-spored, radiation-resistant sectors probably arose by mutation elsewhere in the genome, but alternatively may represent multiple recombination events or deletion of part of one copy of the duplicated region. Loss of the duplicated segment was enhanced by irradiation with ultraviolet light (254 nm). Heterozygosity for a DNA repair mutation at the radB locus may have been involved in the formation of the duplication. It is proposed that translocations are a major cause of nonrandom segregation patterns such as the cosegregation of unlinked markers in Dictyostelium discoideum. Translocations involving all known linkage groups are tabulated and DNA damage by N-methyl-N′-nitro-N-nitrosoguanidine is implicated in the formation of translocations in D. discoideum.
EFFECTS OF NONHOMOLOGY ON BACTERIOPHAGE LAMBDA RECOMBINATION
Authors: Lichten Michael , Fox Maurice S
Published: January 2021

When crosses are performed under conditions severely restricting DNA synthesis, the presence of DNA sequence nonhomologies in the lac region of λplac5 limits the parental material contribution to and the yield of phage recombinant in a region bracketed by the nonhomologies. These observations are consistent with the expectation of a role for branch migration in the formation of heteroduplex structures under these conditions. Under conditions permissive for DNA replication, bracketing a region with nonhomologies has an only modest effect on the yield of recombinants within that interval. In addition, recombinants within such a bracketed interval manifest an excess of coincident exchange events in an adjacent region. These observations suggest the possibility that, under conditions permissive for DNA replication, regions of nonhomology can be included in heteroduplex structures.
CHROMOSOMAL LOCATION OF GENES CONTROLLING FLAVONOID PRODUCTION IN HEXAPLOID WHEAT
Authors: Neuman Paula R , Waines J G , Hilu K W , Barnhart D
Published: January 2021

Two-dimensional paper chromatography was performed on methanol extracts of leaves of hexaploid bread wheat, Triticum aestivum L. em. Thell. cultivar Chinese Spring, and of the available nullisomic-tetrasomic compensating lines, the tetrasomic lines and the ditelocentric lines. The chromatograms had 27 spots identified as flavonoids and six representing phenolic acids. Some of the areas were complex and contained more than one compound. Four flavonoids were identified as under the control of gene(s) on chromosome arms 1DS, 4DL, 5AS and 6BS. A phenolic glycoside was concluded to be controlled by a gene(s) on chromosome arm 7BL. Gene(s) on chromosome arm 4DL affected the amount of compounds in two other spots, and gene(s) on chromosome arm 4BS reduced the level of all flavonoid compounds. The individual compounds in some of the complex spots may be under the control of gene(s) on homoeologous chromosomes.
REVERTANTS OF A TRANSCRIPTION TERMINATION MUTANT OF YEAST CONTAIN DIVERSE GENETIC ALTERATIONS
Authors: Kotval Jeroo , Zaret Kenneth S , Consaul Sandra , Sherman Fred
Published: January 2021

Revertants of the cyc1-512 transcription termination mutant of the yeast Saccharomyces cerevisiae were isolated and subjected to a detailed genetic analysis. The cyc1-512 mutation previously was shown to be a 38-base pair deletion that causes only 10% of the normal steady-state levels of CYC1 mRNA and of the CYC1 gene product, iso-1-cytochrome c. Forty-one cyc1-512 revertants were classified by their content of iso-1-cytochrome c and by their genetic properties in meiotic crosses. Many of the revertants contain local genetic changes that either partially or completely restore the level of iso-1-cytochrome c. One revertant was shown to contain an unlinked extragenic suppressor, designated sut1, that causes partial suppression of the transcription termination defect. Four revertants of cyc1-512 contain chromosomal rearrangements with breakpoints that are tightly linked to the CYC1 locus; these include one duplication, one possible inversion, and two reciprocal translocations. Detailed genetic mapping demonstrated that one of the reciprocal translocations is between the right arms of chromosomes X and XII, with a breakpoint mapping 3′ to the CYC1 locus. These results indicate that the defect in transcription termination in cyc1-512 can be restored in a variety of ways, including the translocation of different chromosomal regions to the 3′ end of the CYC1 locus, local changes presumably at or near the original defect, and by mutation at another locus distinct from CYC1.
SELECTION IN PLANT POPULATIONS OF EFFECTIVELY INFINITE SIZE. V. BIALLELIC MODELS OF TRIOECY
Authors: Gregorius H R , Ross M D , Gillet E M
Published: January 2021

A one-locus two-allele model of trioecy (presence of hermaphrodites, males and females in one population) is considered, in order to study the conditions for the persistence of this system. All possible assignments of the three sex types to the three genotypes are considered. This leads to three different modes of inheritance of trioecy, namely (a) females heterozygous, (b) males heterozygous and (c) hermaphrodites heterozygous, where in each mode each of the remaining two sex types is homozygous for one of the alleles. For mode (c) trioecy is always persistent, and the dependence of the sex ratio (for the three sex types) on the ovule and pollen fertilities and on the hermaphrodite selfing rate is specified. For the other two modes, (a) and (b), trioecy is not protected, i.e., it may not persist for any fertilities, viabilities or selfing rates. Thus, in this situation it is important to study the conditions under which the "marginal" systems of sexuality of trioecy, i.e., hermaphroditism, dioecy and gynodioecy in mode (a), and hermaphroditism, dioecy and androdioecy in mode (b), may become established. The results show that each marginal system may evolve from each other via trioecy. The evolution of dioecy is easier in mode (a) than in (b), so that female heterogamety would be expected to occur more often than male heterogamety in the present model. Under some conditions the breeding system obtained in equilibrium populations may depend on the initial genotype frequencies.—The necessity of considering modes of inheritance for sexual polymorphisms is demonstrated by comparing our results with those obtained from an evolutionary stable strategy (ESS) analysis of a purely phenotypic model.
MATERNAL-ZYGOTIC LETHAL INTERACTIONS IN DROSOPHILA MELANOGASTER: ZESTE-WHITE REGION SINGLE-CISTRON MUTATIONS
Authors: Robbins Leonard G
Published: January 2021

Thirty-eight mutations in 13 essential loci in the zeste-white region were tested for interacting maternal and zygotic gene activity. Maternal mutant heterozygosity provided a partial maternal defect and position-effect variegation was used to alter the level of zygotic gene activity. This method yields a minimum estimate of the number of genes for which zygotic development depends upon both gene products stored in the egg and gene products synthesized in the zygote. Lethal interactions were found for one or more alleles at 10 of the 13 loci. The implications of these observations with respect to gene regulation and developmental sequence are considered.
FURTHER EVIDENCE FOR A POLYMORPHISM IN GAMETIC SEGREGATION IN THE TETRAPLOID TREEFROG HYLA VERSICOLOR USING A GLUTAMATE OXALOACETIC TRANSAMINASE LOCUS
Authors: Danzmann Roy G , Bogart James P
Published: January 2021

Intra- and interspecific cross combinations between the tetraploid treefrog Hyla versicolor, and between H. versicolor and the diploid treefrog Hyla chrysoscelis were performed. Progeny phenotypes resulting from these crosses were examined electrophoretically using a polymorphic glutamate oxaloacetic transminase (GOT-1) locus, to determine the mechanism of chromosome segregation in H. versicolor, and to test theoretical expectations for isozyme expression in interspecific (2n × 4n or 4n × 2n) hybrids. In some intraspecific tetraploid crosses progeny phenotypes fit a disomic mode of segregation, whereas in other crosses a tetrasomic mode of segregation was the most probable. Additional crosses produced phenotypic ratios that conformed to either a disomic or tetrasomic mode of segregation. These results suggest that a polymorphism, with respect to segregation of gametes, exists in H. versicolor, resulting from differences in chromosome pairings during meiosis I. This polymorphism in gametic segregation occurred in both sexes. Certain crosses, however, produced phenotypic ratios that did not conform to any chromosome segregation model. Progeny phenotypes observed from most interspecific crosses conformed to expected interspecific isozyme staining intensity models. Symmetrical heterozygotes, representing either a single dose for both alternate alleles or double doses for both alternate alleles, were also observed. Such phenotypes are unexpected in triploid progeny. A null allele was postulated to account for the aberrant segregation ratios and phenotypes observed in certain intra- and interspecific crosses.
USE OF NYSTATIN-RESISTANT MUTATIONS IN PARASEXUAL GENETIC ANALYSIS IN DICTYOSTELIUM DISCOIDEUM
Authors: Kasbekar Durgadas P , Madigan Sanford , Katz Eugene R
Published: January 2021

Nystatin-resistant mutations exhibit extreme sensitivity to 1.3 mm coumarin. The mutations fall into three complementation groups so it is possible to select for nonallelic mutations conferring sensitivity to coumarin by selection on nystatin-containing nutrient agar plates. Complementation between such coumarin-sensitive mutations allows the selection of diploids on coumarin-containing nutrient agar. Two of the nystatin resistance genes, nysB and nysC, have been mapped tentatively to the previously unmarked linkage group V.
GENETIC VARIATION IN PROTEINS: COMPARISON OF ONE-DIMENSIONAL AND TWO-DIMENSIONAL GEL ELECTROPHORESIS
Authors: McLellan Tracy , Ames Giovanna Ferro-Luzzi , Nikaido Kishiko
Published: January 2021

Two proteins with known characteristics on one-dimensional gels were studied by two-dimensional electrophoresis to compare the sensitivities of the two methods in detecting genetic variation. Two-dimensional electrophoresis was found to be less sensitive than several types of one-dimensional gels in distinguishing variants of both proteins. Denaturation of proteins in urea in the two-dimensional method makes it possible to distinguish closely related proteins that differ from each other by units of charge. Many more types of variation in protein sequences can be distinguished on one-dimensional gels in the absence of denaturants. The estimates of heterozygosity based on two-dimensional gels are lower than those based on other methods, at least in part, because of the limited types of sequence differences that can be detected on two-dimensional gels. The application of two-dimensional electrophoresis to the measurement of genetic variation and to the detection of new mutations should be made carefully, in view of the limited sensitivity of the method in finding differences in sequence.
GENETIC EFFECTS OF UV IRRADIATION ON EXCISION-PROFICIENT AND -DEFICIENT YEAST DURING MEIOSIS
Authors: Resnick Michael A , Game John C , Stasiewicz Stanley
Published: January 2021

The lethal and recombinational responses to ultraviolet light irradiation (UV) by excision-proficient (RAD  +) and deficient strains (rad1) of Saccharomyces cerevisiae has been examined in cells undergoing meiosis. Cells that exhibit high levels of meiotic synchrony were irradiated either at the beginning or at various times during meiosis and allowed to proceed through meiosis. Based on survival responses, the only excision repair mechanism for UV damage available during meiosis is that controlled by the RAD1 pathway. The presence of pyrimidine dimers at the beginning of meiosis does not prevent cells from undergoing meiosis; however, the spore products exhibit much lower survival than cells from earlier stages of meiosis. The reduced survival is probably due to effects of UV on recombination. Meiotic levels of gene conversion are reduced only two to three times in these experiments; however, intergenic recombination is nearly abolished after a dose of 4 J/m2 to the rad1 strain. Exposure to 25 J/m2 had little effect on the wild-type strain. Since normal meiotic reciprocal recombination is generally considered to involve gene conversion-type intermediates, it appears that unrepaired UV damage dissociates the two processes. These results complement those obtained with the mei-9 mutants of Drosophila which also demonstrate a dissociation between gene conversion and reciprocal recombination. These results are consistent with molecular observations on the UV-irradiated rad1 strain in that there is no excision of pyrimidine dimers or exchange of dimers during meiosis.
EXPRESSION OF MATERNALLY AND EMBRYONICALLY DERIVED HYPOXANTHINE PHOSPHORIBOSYL TRANSFERASE (HPRT) ACTIVITY IN MOUSE EGGS AND EARLY EMBRYOS
Authors: Kratzer Paul G
Published: January 2021

X-chromosome activity in early mouse development has been studied by a gene dosage method that involves measuring the activity level of the X-linked enzyme hypoxanthine phosphoribosyl transferase (HPRT) in single eggs and embryos from XO females and from females heterozygous for In(X)1H, a paracentric inversion of the X chromosome. The HPRT activity in oocytes increased threefold over a 24-hr period beginning after ovulation. Afterward, the activity plateaued in unfertilized eggs but continued to increase for at least 66 hr in presumed OY embryos. Both before and after ovulation, the level of activity in unfertilized eggs from In(X)/X females was twice that from XO females, and the distributions of activity in eggs for both sets of females remained unimodal. Beginning with the two-cell stage, distributions of activity for embryos from In(X)/X females were trimodal, which is evidence for embryonic activity. It is proposed that activation of a maternal mRNA or proenzyme is responsible for the HPRT activity increase in oocytes and early embryos and is supplemented by dosage-dependent activity of the embryonic Hprt gene as early as the two-cell stage.