bluuebunny/crossref_metadata_2025 huggingface dataset:
Accurate contact resistance characterization for thermal conductivity measurement with the Heat Flow Meter method
Authors: Fustinoni D , Vitali L , Gramazio P , Niro A
Published: April 2021

A common method to measure the thermal conductivity of low-conductive materials is to impose a known temperature difference across the thickness of the specimen, and to measure the resulting heat flow once steady-state conditions are reached. In particular, international standards, i.e. ASTM C518 and ISO 8301, define the characteristics of the guarded Heat Flow Meter apparatus and its measurement procedure. However, the actual measured quantity is the overall thermal resistance, which is given by the series of the contact resistance between the specimen and the temperature-controlled clamps, and the resistance of the specimen itself. Thus, the contact resistance must be correctly quantified in order to retrieve an accurate measurement. To this end, common practices are either to rely on a database of known contact resistances for material classes, or to use the “double thickness” method, which allows to eliminate the contribution of the contact resistance by carrying out the measurement on two specimens of the same material, but different thickness. While the first method is rather useless for accurate and reliable measurements, especially of unknown or innovative materials, the latter works only if the contact resistances, and therefore the surface finish, are the same for every surface of the specimen set. This paper presents an analysis of the uncertainties associated with the evaluation of the contact resistance carried out on several samples, and proposes a method to reduce such uncertainties, i.e. by inserting elastic thermal pads of known thermal conductivity between the specimen and the instrument. The results of the validation of the method are also shown, with an analysis on the improvement of the measurement accuracy for specimens with high roughness and irregular surfaces, or with conductivities beyond the instrument declared range.
Numerical Study on Thermal and Fluid Dynamic Behavior of Confined Impinging Slot Jets with Nanofluids in Partially Filled Configuration of Metal Foam
Authors: Buonomo B , di Pasqua A , Manca O , Nappo S
Published: April 2021

In this work a numerical analysis on confined slot impinging jets constituted by a partially filled configuration of metal foam in mixed convection is illustrated. The employed working fluids are pure water or Al2O3/water based nanofluids A two-dimensional model is constructed and several Peclet numbers (equal to 100, 200, 350, 750, 1500) are assumed. Rayleigh numbers is fixed equal to 30000. The nanoparticle volume concentrations are in a range from 0% to 4% and the nanoparticle diameter is considered equal to 30nm. The target surface is characterized by a constant temperature, evaluated according to the value of Rayleigh number. The distance of the target surface is five times greater than the slot jet width. Three different values of ratio between the total system and the metal foam length have been assumed. The thermal and fluid-dynamic properties of nanofluids are estimated by a single-phase model approach. The model of local thermal non equilibrium (LTNE) is assumed in order to replicate the behavior of the metal foam characterized by a number of pores per inch (PPI) equal to 20 and a porosity of 0.9005. Results show increasing values of the convective heat transfer coefficients for increasing values of Peclet number and nanoparticle concentration. This behaviour is more evident at low Peclet number values. In conclusion, the ratio between the thermal and pumping power is calculated in order to find a trade-off between the increase of heat transfer and pressure drop.
Experimental evaluation of the thermal conductivity for additive manufactured materials. New test facility concept and preliminary tests
Authors: Bianco N , Mastrullo R , Mauro A W , Viscito L
Published: April 2021

Items for heat transfer made by metal foams or additive manufactured structures allow to create special components for several applications (i.e. fast response PCM, complex and light HEXs working at high temperatures for the aerospace sector). For their design thermo-physical properties data are required, such as thermal conductivity. To accurately measure this parameter with conventional procedures for metallic items (e.g. flash methods), the specific heat and density should be measured each time depending on the actual composition of the porous media (estimation is not yet reliable and porosity not known). The scope of this paper is to validate a test facility and the relative method for the data reduction to proof the possibility to measure directly the thermal conductivity with samples of small size. The experiments, carried-out with square samples (30×30 mm2), allow to measure a range of thermal conductivity between 5 and 50 W/m K. The main aspect of the experimental method is the calibration of the heat losses towards the environment by means of a reverse technique. The assessment of the results against samples of known materials was good.
Experimental study of mitigation systems to prevent Thermal Runaway of Li-ion Batteries
Authors: D’Annibale Francesco , Menale Carla
Published: April 2021

Li-ion batteries have experienced a widespread deployment due to the strong interest in electrochemical devices capable of storing a large amount of energy in small volumes and supplying high powers when required. However, besides those advantages, this technology still presents several unsolved issues, especially regarding the safety aspects. These devices can, in fact, experience thermal runaway if the generated thermal power is not adequately dispersed, and this can occur when the cell / battery is subjected to abuse conditions (mechanical, electrical or thermal abuses).

The experimental study was carried out using a full-scale hardware simulator, capable of simulating the thermal behavior of a battery pack, where electrically heated elements replaced real Li-ion cells. This expedient guarantees a high reproducibility of the working conditions and consequently a higher reliability of the measured data.

The hardware simulator allows to reproduce the thermal behavior under normal operating conditions, and under abuse conditions which can lead to thermal runaway.

The present work reports the results of the tests that have been carried out by reproducing the abuse conditions in one cell inside a battery module; the abused cell is heated with a high power (from 100 to 500 W for cells with a maximum heat loss of 30 W under normal operating conditions) and the efficiency of different cooling systems is checked both in limiting the temperature of the abused cell and in preventing the propagation of heat to the adjacent cells. In particular, different fluids, different fluid speeds and different mitigation methods have been tested.
SBO analysis of a generic PWR-900 with ASTEC and MELCOR codes
Authors: Maccari Pietro , Mascari Fulvio , Ederli Stefano , Manservisi Sandro
Published: April 2021

After the Fukushima accident, the interest of the public to nuclear safety has growth and the international technical nuclear community has increased his attention in the investigation and the characterization of Severe Accident (SA) scenarios. In order to simulate the different, complex and multi-physical phenomena involved in a SA, computational tools, known as SA codes, have been developed in the last decades. In order to give some insights on the modelling capabilities of these tools and the differences in the calculation results, also related to the user-effect, an analysis of an unmitigated Station Black Out (SBO) occurring in a generic Western three-loops PWR 900 MWe has been carried out by the authors in the framework of the NUGENIA TA-2 ASCOM project. The simulation results of ASTEC code (study carried out with ASTEC V2, IRSN all rights reserved, [2019]), developed by IRSN, and MELCOR 2.2 code, developed by SANDIA for USNRC, have been compared and analyzed. The SBO scenario considered takes into account the intervention of the accumulators as only accident mitigation strategy. Several figures of merits related to the thermal-hydraulic (e.g. primary pressure, cladding temperature, etc.) and to the core degradation (e.g. hydrogen production, etc.) have been considered to describe the accident evolution until the vessel failure, for the two codes comparison.
Propagation of geometric uncertainties in heat transfer problems solved by RBF-FD meshless method
Authors: Zamolo R , Parussini L , Nobile E
Published: April 2021

The design of engineering components must take into account the manufacturing tolerances of production processes since they lead to uncertainties in the behaviour of the products. It is therefore of valuable practical interest to quantify such uncertainties, with particular reference to problems involving geometrical uncertainties of the boundaries. This task is carried out in the present work by coupling the Non-Intrusive Polynomial Chaos (PC) method, employed for the quantification of uncertainties, with a Radial Basis Function Finite Differences (RBF-FD) meshless method, employed for the numerical simulations. The PC method with the Non-Intrusive formulation allows the use of existing deterministic solvers for the accurate prediction of the sought random response, i.e., the statistic moments of the involved variables. The RBF-FD method is therefore employed as a black box solver for the required set of problems defined over deterministic domains. The main advantage of the RBF-FD meshless method over traditional mesh-based methods is its capability of easily deal with practical problems defined over complex-shaped domains since no traditional mesh is required. The geometrical flexibility of the RBF-FD is even more advantageous in the context of geometric uncertainty quantification with the Non-Intrusive PC method since different solutions over different geometries are required. The applicability of the proposed approach to practical problems is then presented through the prediction of geometric uncertainty effects for a tube heat exchanger under natural convection where a 2D steady incompressible flow is considered.
Thermal characterisation of Triple Concentric Tube Heat Exchangers by applying parameter estimation: direct problem implementation
Authors: Vocale P , Malavasi M , Cattani L , Bozzoli F , Pelacci M , Rainieri S
Published: April 2021

Heat transfer enhancement in heat exchangers’s design represents a key technological challenge because of the increase in the cost of energy and raw materials. A promising technology is represented by the triple tube heat exchangers, in which the heat transfer is enhanced in comparison with the traditional double tube heat exchangers, due to the larger heat transfer area per unit length. Among the different methodologies that can be adopted to assess the performance of the triple tube heat exchangers, parameter estimation procedure represents a promising tool, since it has been successfully applied in many disciplines of engineering. To apply this inverse technique, it is mandatory defining the direct problem, which for the issue here addressed allows evaluating the outlet temperatures of the fluids flowing in the heat exchanger. Since in a triple tube heat exchanger there are three fluids, the approach based on the evaluation of the logarithmic mean temperature difference is no longer valid and an alternative procedure has to be followed. In the present analysis a numerical model for the performance evaluation of triple tube heat exchangers is presented. The validation of the proposed numerical model, carried out by adopting the analytical model available in literature, highlights that the model can be considered accurate and reliable. Moreover, the computational time required to solve the set of equations is very limited.
Preliminary analysis of the influence of environmental boundary conditions on convective heat transfer coefficients
Authors: Evangelisti Luca , Guattari Claudia , Rubeis Tullio de
Published: April 2021

In this contribution, a hot box apparatus was used to investigate convective heat transfers through an experimental setup composed of a heat-flow sensor, air and surface temperature probes installed on the wall tested in the hot box and a hot-wire anemometer. The air near the wall was indirectly moved by means of a forced convection system through which the air velocity can be modified to simulate different environmental conditions. The hot box apparatus was used in order to investigate the influence of the air velocity on internal convective heat transfer coefficients (hc), under natural/mixed convection conditions. The Standard ISO 6946 suggests a typical internal convective heat transfer coefficient equal to 2.5 W/m2K when horizontal heat fluxes occur. No detailed information about this value are reported in the Standard. So, the final aim of this study is to assess the applicability of the internal convective heat transfer coefficient value proposed by ISO 6946 under different air velocity values, quantifying how hc varies as air velocity changes.
Environmental Effect on Temperature Measurement in Natural Gas Network Balance
Authors: Arpino F. , Canale L. , Cortellessa G. , D’Alessio R. , Dell’Isola M. , Ficco G. , Moretti L. , Vigo P. , Zuena F.
Published: April 2021

Accurate temperature measurements are essential for accounting and balancing natural gas in transmission and distribution networks. In fact, in order to convert the gas volumes measured at operational conditions into standard reference ones, the accurate knowledge of both the thermodynamic conditions of the gas (i.e. temperature and pressure) and its chemical composition is necessary. In the case of large flow-meters, even small measurement errors (e.g. deriving from difference between the ambient temperature and the temperature of the fluid) can become relevant in terms of “unaccounted for gas”, especially when they do not find adequate compensation during the annual balancing of the network. To this aim it is necessary to carefully evaluate the systematic errors affecting temperature measurement which depend on instrumentation metrological characteristics as well as on thermo-fluid dynamic issues. In some cases, thermal insulation of the flow-meter and both upstream and downstream measuring stretches should be necessary. In this paper the authors present the results of an experimental study on the installation effects of temperature probes in closed conduits, performed at different operating conditions of natural gas transmission networks and aimed at estimating the typical random and systematic effects, and proposing optimal installation and operative solutions.
Influence of the Thermophysical Model on the CFD Analysis of Oil-Cooled Transformer Windings
Authors: Salerno Elisabetta , Leonforte Adriano , Angeli Diego
Published: April 2021

A disc-type winding of an oil-immersed power transformer is modeled with Computational Fluid Dynamics. Different approaches are implemented to evaluate the feasibility of the Boussinesq approximation: (i) constant fluid properties, (ii) variable viscosity and thermal diffusivity and (iii) temperature-dependent fluid properties. Temperature and flow distributions are reconstructed and put into relation with physical phenomena and model assumptions. Their comparison suggests that numerical results are fairly sensitive to the thermophysical model as long as the buoyancy force is a relevant component of the flow. Nonetheless, all the cases converge to very close predictions of the hot-spot value and location, with possibly positive implications for the use of reference parameters when deriving flow and heat transfer correlations for this topic.
Biophysical and policy factors predict simplified crop rotations in the US Midwest
Authors: Socolar Yvonne , Goldstein Benjamin R , de Valpine Perry , Bowles Timothy M
Published: April 2021

Over 70% of the 62 million hectares of cropland in the Midwestern United States is grown in corn-based rotations. These crop rotations are caught in a century-long simplification trend despite robust evidence demonstrating yield and soil benefits from diversified rotations. Our ability to explore and explain this trend will come in part from observing the biophysical and policy influences on farmers’ crop choices at one key level of management: the field. Yet field-level crop rotation patterns remain largely unstudied at regional scales and will be essential for understanding how national agricultural policy manifests locally and interacts with biophysical phenomena to erode—or bolster—soil and environmental health, agricultural resilience, and farmers’ livelihoods. We developed a novel indicator of crop rotational complexity and applied it to 1.5 million fields across the US Midwest. We used bootstrapped linear mixed models to regress field-level rotational complexity against biophysical (land capability, precipitation) and policy-driven (distance to the nearest biofuel plant and grain elevator) factors. After accounting for spatial autocorrelation, there were statistically clear negative relationships between rotational complexity and biophysical factors (land capability and precipitation during the growing season), indicating decreased rotation in prime growing areas. A positive relationship between rotational complexity and distance to the nearest biofuel plant suggests policy-based, as well as biophysical, constraints on regional rotations. This novel RCI is a promising tool for future fine-scale rotational analysis and demonstrates that the United States’ most fertile soils are the most prone to degradation, with recent policy choices further exacerbating this trend.
An enhanced periosteum structure/function dual mimicking membrane for in-situ restorations of periosteum and bone
Authors: Laijun Liu , Yu Zhang , Chaojing Li , Jifu Mao , Fujun Wang , Lu Wang
Published: April 2021

Periosteum plays a pivotal role in bone formation and reconstruction. The ideal repair process for critical-size bone defects with periosteum damage is to induce regeneration of periosteum tissue and the subsequent bone regeneration derived by the periosteum. Inspired by the bilayer structure of the natural periosteum, we develop a periosteum structure/function dual mimicking membrane for the in-situ restoration of periosteum and bone tissue. Among them, the macroporous fluffy guiding layer (TPF) simulates the fibrous layer of the natural periosteum, which is conducive to infiltration and oriented growth of fibroblasts. And the extracellular matrix-like bioactive layer (TN) simulates the cambium layer of the natural periosteum, which significantly enhances the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells. A middle dense layer (PC) connects the above two layers and has the function of preventing the invasion of soft tissues while enhancing the biomimetic periosteum. In vivo restoration results show that the tri-layer biomimetic periosteum (TPF/PC/TN) has an outstanding effect in promoting the regeneration of both vascularized periosteum and bone at the same time. Therefore, the enhanced biomimetic periosteum developed in this research has a great clinical value in the efficient and high-quality reconstruction of critical-size bone defects with periosteum damage.
Surface Physical Properties of Ion Beam Sputtered Copper Thin Films on Poly Tetrafluoroethylene
Authors: Atta A , Abdeltwab E , Bek A
Published: April 2021

In this study thin copper (Cu) films are deposited on poly tetrafluoroethylene (PTFE) substrate using ion beam sputtering technique. The films are characterized using Raman spectroscopy, UV–VIS spectroscopy and atomic force microscope (AFM) techniques. The Raman spectrum shows some decrease in the intensities of Raman bands for Cu/PTFE film than pristine PTFE. UV–VIS transmittance spectra display that the optical transmission reduces from ~75% for pristine PTFE to ~0.20% after 60 min of deposition due to Cu nanoparticles dispersed in PTFE. The surface roughness is increased from 39.4 nm for PTFE to 75.9 nm, while the adhesion force is increased from 9.6 nN to 14.7 nN and Young’s modulus is enhanced from 0.58 GPa to 1.46 GPa after 40 min of Cu deposition time. The DC electrical conductivity at an applied voltage of 200 V is improved from 3.88 × 10–8 S.cm−1 for PTFE to 5.3 × 10–8 S.cm−1 after 60 min of deposition at room temperature. The fabricated Cu/PTFE films exhibit excellent surface properties, which demote that Cu/PTFE films could serve as a low cost material for a broad range of electrical and charge storing devices.
Microstructure and fatigue damage mechanism of 6082-T6 aluminium alloy welded joint
Authors: Zhu Minqi , Yang Shanglei , Bai Yishan , Fan Cong
Published: April 2021

In this paper, 6mm thick 6082-T6 high-strength aluminium alloy is taken as the research object, and CLOOS ROMAT-3500 industrial robot MIG welder is used for welding. High-cycle fatigue test is carried out on welded joint and 6082-T6 base metal. Microstructure, microhardness, tensile properties and fatigue properties are studied, and fatigue fracture is observed and analyzed. The test results show that: equiaxed crystals exist in the center of the weld. Broken equiaxed crystals are found in the weld due to stirring in the molten pool, a large number of pore and columnar crystal layers are found at the junction of the two beads. A small amount of pore and cellular dendrite are found in the fusion zone. A softening zone with a minimum hardness of 65.5HV exists in the heat affected zone(HAZ). The conditional fatigue limits for base metal and weld specimens are 77.26MPa and 48.69MPa at the set target cycle of 107 respectively. In fatigue fracture, there are a lot of cleavage fracture characteristics and ductile fracture characteristics. The crack initiation is quasi-cleavage fracture characteristic. In the past studies, I have studied the fatigue life of joints, but as the research progresses, I believe that the fatigue behavior and fatigue damage mechanism plays an important role in fatigue life. In this paper, Fatigue fracture process is analyzed by correlation calculation of stress intensity factor. Two crack initiation modes are proposed based on the welding process. The first is fatigue crack initiation caused by stress concentration at the grain boundary where hydrogen elements converged, the second is fatigue crack initiation caused by the gap between equiaxed and columnar crystals inside and outside the central pore of the weld.
Surface characteristics and osteocompatibility of titanium preserved in a ZnS@BSA-containing storage solution
Authors: Tang Zehua , Tang Kaiming , Liu Yao , Zhu Wenqing , Qiu Jing
Published: April 2021

This study aimed to the preparation of a storage solution containing zinc sulfide particles encapsulated in bovine serum albumin (ZnS@BSA) and its application to improve surface characteristics and osteocompatibility of pure and SLA titanium surfaces. The analysis of surface characteristics including surface topography, elemental distribution and protein amounts confirmed that ZnS@BSA particles were successfully adsorbed on the two titanium surfaces without changing the original morphology. Assays of wettability showed that titanium surfaces preserved in ZnS@BSA solution had superior hydrophilicity compared with control groups. In vitro experiments demonstrated that the titanium surfaces preserved in ZnS@BSA solution significantly promoted the proliferation, adhesion and differentiation of MC3T3-E1 cells. The study therefore concluded that the ZnS@BSA solution could improve the bioactivity of titanium surface and exhibit the potential to be a new type of titanium implant storage solution.
A generalized framework for analytic regularization of uniform cubic B-spline displacement fields
Authors: Shah Keyur D , Shackleford James A , Kandasamy Nagarajan , Sharp Gregory C
Published: April 2021

Image registration is an inherently ill-posed problem that lacks the constraints needed for a unique mapping between voxels of the two images being registered. As such, one must regularize the registration to achieve physically meaningful transforms. The regularization penalty is usually a function of derivatives of the displacement-vector field and can be calculated either analytically or numerically. The numerical approach, however, is computationally expensive depending on the image size, and therefore a computationally efficient analytical framework has been developed. Using cubic B-splines as the registration transform, we develop a generalized mathematical framework that supports five distinct regularizers: diffusion, curvature, linear elastic, third-order, and total displacement. We validate our approach by comparing each with its numerical counterpart in terms of accuracy. We also provide benchmarking results showing that the analytic solutions run significantly faster—up to two orders of magnitude—than finite differencing based numerical implementations.
Training sets based on uncertainty estimates in the cluster-expansion method
Authors: Kleiven David , Akola Jaakko , Peterson Andrew A , Vegge Tejs , Chang Jin Hyun
Published: April 2021

Cluster expansion (CE) has gained an increasing level of popularity in recent years, and its applications go far beyond its original root in binary alloys, reaching even complex crystalline systems often used in energy materials research. Similar to other modern machine learning approaches in materials science, many strategies have been proposed for training and fitting the CE models to first-principles calculation results. Here, we propose a new strategy for constructing a training set based on their relevance in Monte Carlo sampling for statistical analysis and reduction of the expected error. The CE model constructed from the proposed approach has lower dependence on the specific details of the training set, thereby increasing the reproducibility of the model. The same method can be applied to other machine learning approaches where it is desirable to sample relevant configurational space with a small set of training data, which is often the case when they consist of first-principles calculations.
On the number of discrete chains
Authors: Palsson Eyvindur , Senger Steven , Sheffer Adam
Published: April 2021

We study a generalization of the Erdős unit distance problem to chains of

k
k

distances. Given

P

,

\mathcal {P},

a set of

n
n

points, and a sequence of distances

(

δ
1

,
…
,

δ
k

)

(\delta _1,\ldots ,\delta _k)

, we study the maximum possible number of tuples of distinct points

(

p
1

,
…
,

p

k
+
1

)
∈

P

k
+
1

(p_1,\ldots ,p_{k+1})\in \mathcal {P}^{k+1}

satisfying

|

p
j

p

j
+
1

|

=

δ
j

|p_jp_{j+1}|=\delta _j

for every

1
≤
j
≤
k

1\le j \le k

. We study the problem in

R

2

\mathbb {R}^2

and in

R

3

\mathbb {R}^3

, and derive upper and lower bounds for this family of problems.
Arrhythmogenesis in the aged heart following ischaemia–reperfusion: role of transient receptor potential vanilloid 4
Authors: Peana Deborah , Polo-Parada Luis , Domeier Timothy L
Published: April 2021

Aims

Cardiomyocyte Ca2+ homoeostasis is altered with ageing and predisposes the heart to Ca2+ intolerance and arrhythmia. Transient receptor potential vanilloid 4 (TRPV4) is an osmotically activated cation channel with expression in cardiomyocytes of the aged heart. The objective of this study was to examine the role of TRPV4 in Ca2+ handling and arrhythmogenesis following ischaemia–reperfusion (I/R), a pathological scenario associated with osmotic stress.

Methods and results

Cardiomyocyte membrane potential was monitored prior to and following I/R in Langendorff-perfused hearts of Aged (19–28 months) male and female C57BL/6 mice ± TRPV4 inhibition (1 μM HC067047, HC). Diastolic resting membrane potential was similar between Aged and Aged HC at baseline, but following I/R Aged exhibited depolarized diastolic membrane potential vs. Aged HC. The effects of TRPV4 on cardiomyocyte Ca2+ signalling following I/R were examined in isolated hearts of Aged cardiac-specific GCaMP6f mice (±HC) using high-speed confocal fluorescence microscopy, with cardiomyocytes of Aged exhibiting an increased incidence of pro-arrhythmic Ca2+ signalling vs. Aged HC. In the isolated cell environment, cardiomyocytes of Aged responded to sustained hypoosmotic stress (250mOsm) with an increase in Ca2+ transient amplitude (fluo-4) and higher incidence of pro-arrhythmic diastolic Ca2+ signals vs. Aged HC. Intracardiac electrocardiogram measurements in isolated hearts following I/R revealed an increased arrhythmia incidence, an accelerated time to ventricular arrhythmia, and increased arrhythmia score in Aged vs. Aged HC. Aged exhibited depolarized resting membrane potential, increased pro-arrhythmic diastolic Ca2+ signalling, and greater incidence of arrhythmia when compared with Young (3–5 months).

Conclusion

TRPV4 contributes to pro-arrhythmic cardiomyocyte Ca2+ signalling, electrophysiological abnormalities, and ventricular arrhythmia in the aged mouse heart.
Understanding students’ motivation in L2 collaborative writing
Authors: Chen Wenting
Published: April 2021

Although research about the potential learning outcome of collaborative writing in L2 or foreign language education has proliferated in the last few decades, little is known about students’ motivation in collaborative writing. This case study seeks to explore higher-proficiency (HP) students’ motivation in L2 collaborative writing, as well as factors influencing their motivation. The findings reveal that students with similar proficiency (HP) could have different levels of motivation, which may affect their participation. This study also found that knowledge of collaborative writing, previous beliefs and experiences of pair/group work, and perceived value of the role in the partnership were three major factors that influence students’ motivation in collaborative writing. This study makes several recommendations from a motivational perspective about how best to implement collaborative writing tasks in L2 classes.
THE GENETIC BASIS FOR CONSTRUCTING SELECTION INDEXES
Authors: Hazel L N
Published: April 2021

"The key is man's power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him."—Darwin, p. 35, sixth edition of The Origin of Species. 1920.
POLYMORPHISM FOR DIMERIZING ABILITY AT THE ESTERASE-5 LOCUS IN DROSOPHILA PSEUDOOBSCURA
Authors: Cobbs Gary
Published: April 2021

Three new alleles are reported at the esterase-5 locus of Drosophila pseudoobscura. All three of these alleles are different from those previously reported in their ability to dimerize. One allele will not form heterodimers or homodimers and exists only as a monomer. A second allele does form heterodimers but will not form homodimers. The third allele forms both hetero- and homodimers as well as forming monomers. Estimates of the frequency of these alleles in a natural population are given. The existence of these is discussed with respect to recently proposed models for a molecular mechanism for heterosis.
TERMINAL REDUNDANCY HETEROZYGOTES INVOLVING THE FIRST-STEP-TRANSFER REGION OF THE BACTERIOPHAGE T5 CHROMOSOME
Authors: Fischhoff David , MacNeil Douglas , Kleckner Nancy
Published: April 2021

Individual progeny of two-factor crosses between A1am and A2am T5 phages give rise to bursts containing more than one type of plaque. The simplest explanation for these mixed bursts is that the A1 and A2 genes are located within the terminally repeated portion of the T5 genome and that the mixed bursts are made by "terminal redundancy heterozygotes". The observation of genetic heterozygosity means that the A1 and A2 genes are repeated intact. This implies that the terminal segments of T5 are genetically interchangeable.
UV MUTAGENESIS IN RADIATION-SENSITIVE STRAINS OF YEAST
Authors: Lawrence Christopher W , Christensen Roshan
Published: April 2021

The yeast Saccharomyces cerevisiae appears to possess a single mutagenic or "error prone" pathway for the repair of UV damage, probably involving the functions of at least seven genes; rev1, rev2, rev3 (Lemontt 1971a), rad6, rad8, rad9 and rad18 (Lawrence et al. 1974; present results). Strains carrying rad6 are the most sensitive to the lethal effects of UV light in this group and double mutants carrying rad6 and either rev1, rev3, rad9 or rad18 are no more sensitive than this single mutant strain. rev3 rad6 double mutant diploids failed to show any UV-induced reversion of the normally highly revertible ochre allele cyc1-9, even though a total of more than 2.5 × 109 viable cells was examined, suggesting that strains of this kind are entirely UV-immutable; spontaneous revertants could be recovered, however.—The rad6 and rev3 gene products would appear to be necessary for all kinds of mutagenic events at all sites within the genome, but the products of the other genes that act in the "errorprone" pathway hage a more restricted role and are involved in the production of only some kinds of mutations. It is suggested that such selectivity arises from the interaction of some repair enzymes with specific nucleotide sequences.
THE UNIT OF SELECTION IN DROSOPHILA MERCATORUM I. THE INTERACTION OF SELECTION AND MEIOSIS IN PARTHENOGENETIC STRAINS
Authors: Templeton Alan R , Sing Charles F , Brokaw Barbara
Published: April 2021

An important problem in population genetics is the determination of the level of genetic organization to which fitness measures can be ascribed that yield an adequate description or prediction of the outcome of selection in populations. To study this problem, we used two strains of Drosophila merca torum (S-1-Im and O-3-Im) that are capable of both sexual and parthenogenetic reproduction, a feature that allows us to experimentally control many factors which affect genetic variability. Both S and O reproduce parthenogenetically by "pronuclear duplication," a mechanism that retains normal meiosis (and hence crossing over and assortment) but results in homozygosity for all loci in a single generation. Since an isozyme survey indicated that S and O differ at a third of their loci, we hypothesized that S and O have adapted in genetically distinct fashions to the genetic environment of total homozygosity. This is tested by breeding females that are S-O hybrids for 100%, 60% and 40% of their genetic backgrounds, and scoring their respective parthenogenetic progenies for four isozyme and two visible markers. The data collected gave evidence for a coadaptation to total homozygosity involving non-additive and non-multiplicative interactions between non-alleles. As the perturbation of the parental coadapted genotypes by meiosis increases (i.e., the greater the degree of S-O hybridity), the level of genetic material which behaves as an additive/multiplicative fitness unit becomes larger. Selective neutrality of genetic variation may be an artifact of our failure to measure the proper genetic unit of selection.
TWO CHROMOSOMAL GENES REQUIRED FOR KILLING EXPRESSION IN KILLER STRAINS OF SACCHAROMYCES CEREVISIAE
Authors: Wickner Reed B , Leibowitz Michael J
Published: April 2021

The killer character of yeast is determined by a 1.4 × 106 molecular weight double-stranded RNA plasmid and at least 12 chromosomal genes. Wild-type strains of yeast that carry this plasmid (killers) secrete a toxin which is lethal only to strains not carrying this plasmid (sensitives). —— We have isolated 28 independent recessive chromosomal mutants of a killer strain that have lost the ability to secrete an active toxin but remain resistant to the effects of the toxin and continue to carry the complete cytoplasmic killer genome. These mutants define two complementation groups, kex1 and kex2. Kex1 is located on chromosome VII between ade5 and lys5. Kex2 is located on chromosome XIV, but it does not show meiotic linkage to any gene previously located on this chromosome. —— When the killer plasmid of kex1 or kex2 strains is eliminated by curing with heat or cycloheximide, the strains become sensitive to killing. The mutant phenotype reappears among the meiotic segregants in a cross with a normal killer. Thus, the kex phenotype does not require an alteration of the killer plasmid. —— Kex1 and kex2 strains each contain near-normal levels of the 1.4 × 106 molecular weight double-stranded RNA, whose presence is correlated with the presence of the killer genome.
THE POPULATION GENETICS OF PARTHENOGENETIC STRAINS OF DROSOPHILA MERCATORUM. II. THE CAPACITY FOR PARTHENOGENESIS IN A NATURAL, BISEXUAL POPULATION
Authors: Templeton Alan R , Carson Hampton L , Sing Charles F
Published: April 2021

Drosophila mercatorum is a bisexual species, but certain strains are capable of parthenogenetic reproduction in the laboratory. We investigated the parthenogenetic capacity of the virgin daughters of females captured from a natural, bisexual population in Hawaii. An isozyme survey indicated the natural population is polymorphic at about 50% of its loci, and its individuals heterozygous at 18% of their loci. The predominant mode of parthenogenesis in D. mercatorum causes homozygosity for all loci in a single generation. Despite this radical change in genetic state, 23% of the virgin female lines produced adult parthenogenetic progeny, and 16% produced parthenogenetic progeny themselves capable of parthenogenetic reproduction. The parthenogenetic rate as measured by the number of parthenogenetic progeny themselves capable of parthenogenesis divided by the number of eggs laid is around 10-5 for the virgin female lines. We argue that one of the major reasons for this low rate is that very few of the impaternate zygotes have a genotype that can survive and reproduce under the genetic conditions imposed by parthenogenetic reproduction. This intense selective bottleneck can be passed in a single generation if enough unfertilized eggs are laid, and once passed is accompanied by a large (perhaps a thousandfold) increase in the rate of parthenogenesis and by modifications in many phenotypic traits such as morphology and behavior.
HIDDEN ALLELES AT THE α-GLYCEROPHOSPHATE DEHYDROGENASE LOCUS IN COLIAS BUTTERFLIES
Authors: Johnson George B
Published: April 2021

By varying polyacrylamide gel pore size, the α-glycerophosphate dehydrogenase locus of Colias butterflies is shown to contain at least five alleles, rather than the two which had been reported previously. Two of the alleles have the same apparent net charge, and presumably are detected electrophoretically because of conformational differences. Additional variation occurs in the isoelectric points of the proteins. It is suggested that electrophoresis employing a single gel of intermediate pore size will fail to discriminate between many alleles, and that the concept of electrophoretic alleles as differing simply in charge may not always be appropriate.

"How does one know what it is one believes

When it's so difficult to know what it is one knows?"

—Jumpers (Stoppard, 1972)
ON THE NATURE OF CIS-ACTING REGULATORY PROTEINS AND GENETIC ORGANIZATION IN BACTERIOPHAGE: THE EXAMPLE OF GENE Q OF BACTERIOPHAGE Λ
Authors: Echols Harrison , Court Donald , Green Linda
Published: April 2021

We note the existence of a "partially cis-acting" regulatory protein of bacteriophage λ: the product of the phage Q gene. We suggest that there may be a complete spectrum from "all cis" to "all trans" for such regulatory proteins. This behavior might arise because a DNA-binding protein either acts at a nearby (cis) site soon after synthesis or becomes "lost" for its trans activity on another genome through nonspecific interactions with DNA. Our proposed explanation provides one evolutionary basis for the linkage of genes for regulatory proteins and the sites at which such proteins act; it also suggests a possible rationale for the "metabolic instability" of certain regulatory proteins.
A POLLEN SELECTION SYSTEM FOR ALCOHOL-DEHYDROGENASE-NEGATIVE MUTANTS IN PLANTS
Authors: Schwartz Drew , Osterman John
Published: April 2021

Exposure of freshly shed maize pollen to allyl alcohol vapors allows selective fertilization by mutant alcohol-dehydrogenase-negative grains. Wild-type pollen grains are killed by the enzymatic conversion of allyl alcohol to the highly toxic acrylaldehyde.
INTERCONVERSION OF YEAST MATING TYPES I. DIRECT OBSERVATIONS OF THE ACTION OF THE HOMOTHALLISM (HO) GENE
Authors: Hicks James B , Herskowitz Ira
Published: April 2021

The HO gene promotes interconversion between a and α mating types. As a consequence, homothallic diploid cells are formed by mating between siblings descended from a single α HO or a  HO spore. In order to determine the frequency and pattern of the mating-type switch, we have used a simple technique by which the mating phenotype can be assayed without losing the cell to the mating process itself. Specifically, we have performed pedigree analysis on descendants of single homothallic spores, testing these cells for sensitivity to α-factor.

The switch from α to a and vice versa is detectable after a minimum of two cell divisions. 50% of the clones tested showed switching by the four-cell stage. Of the four cells descended from a single cell, only the oldest cell and its immediate daughter are observed to change mating type. This pattern suggests that one event in the switching process has occurred in the first cell division cycle. Restriction of the switched mating-type to two particular cells may reflect the action of the homothallism system followed by nonrandom segregation of DNA strands in mitosis.

The mating behavior of cells which have sustained a change in mating type due to the HO gene is indistinguishable from that of heterothallic strains.
F' PLASMIDS FROM HfrH AND HfrC IN recA- ESCHERICHIA COLI
Authors: Ou Jonathan T , Anderson Thomas F
Published: April 2021

We have isolated and characterized a number of clones resulting from matings of HfrH and HfrC cultures of Escherichia coli with auxotrophic recA- E. coli. As in Low's (1968) experiments, the recA- marker prevented integration of F′ episomes into the vegetative chromosomes of the host. Both F′H F′C plasmids contained a great variety of non-selected nutritional markers. However, more F′H plasmids seemed to have expressed F+ characteristics than did F′C plasmids. These characteristics include (i) the presence of F-pili as determined by susceptibility to male-specific phages; (ii) fertility as determined by the merozygote's ability to transfer nutritional markers to an auxotrophic F- strain of E. coli; and (iii) a high degree of inheritability as estimated by the proportion of F′ bacteria to F- bacteria in clones grown in a non-selective medium like broth. This proportion is seen to be affected by both factors that determine the probabilities that daughters of F′ bacteria inherit the episome and from physiological factors that determine the rates of growth of F′ and F- bacteria.
GENETIC CONTROL OF GENE EXPRESSION: INDEPENDENT LOCATION OF Flt(3) AND ITS INTERACTIONS WITH THE MUTABLE V LOCUS IN NICOTIANA
Authors: Sand Seaward A
Published: April 2021

New information has resulted from studies comparing the genetic behavior of two experimental cultures, termed variegated-3 and variegated-1, which arose earlier following an interspecific cross. Phenotypic expression in the plant material involves distinctive variegation patterns of anthocyanin distribution in floral tissues.—The data are consistent with the hypothesis that the genetic constitution of variegated-3 includes a unique and independently segregating regulator component, Flt(3), in addition to the v locus element held in common with variegated-1. Flt(3) has not been generated anew within the variegated-1 genotypes among more than 10,000 observed progeny. Presence of Flt(3) modifies the timing of somatic sectoring events, and is correlated with the capability to produce, in germ cell lines of phenotypically flecked plants, frequent changes at the v locus to a stable, non-variegating, dominant allelic form, V.—The latter process is of special interest because progeny tests of mutant individuals, containing newly-arisen V alleles, fail to reveal continued presence of Flt(3). Thus the mechanism generating V from v appears to be correlated invariably with loss or inactivation of the controllingelementinducing this class of mutations, which is located initially on a different chromosome from that bearing v.
GENETIC MODELS FOR THE ANALYSIS OF DATA FROM THE FAMILIES OF IDENTICAL TWINS
Authors: Nance Walter E , Corey Linda A
Published: April 2021

Genetic models are described which exploit the unique relationships that exist within the families of identical twins to obtain weighted least squares estimates of additive, dominance and epistatic components of genetic variance as well as estimates of the contributions of X-linked genes, maternal effects and three sources of environmental variation. Since all of the relationships required to achieve a resolution of these variance components are contained within each family unit, the model would appear to be superior to previous approaches to the analysis of quantitative traits in man.
EVOLUTION OF HAWAIIAN DROSOPHILIDAE. II. PATTERNS AND RATES OF CHROMOSOME EVOLUTION IN AN ANTOPOCERUS PHYLOGENY
Authors: Yoon J S , Richardson R H
Published: April 2021

The phylogenetic relationships of seven species of the genus Antopocerus (Family Drosophilidae) have been determined by means of a study of the metaphase configurations and polytene chromosomes. Based on biogeographical, behavioral and cytogenetic information, A. longiseta from Molokai is tentatively identified as the primitive species of the genus. The metaphase karyotypes of all Antopocerus species are either five pairs of rod chromosomes and a pair of dots (5R1D), or six rods (6R). Heterochromatin additions converted the dots to rods. Chromosome breakpoints for inversions also are clustered at heterochromatic loci. The chromosome segments between heterochromatic loci may represent sets of functionally related loci, evolving as a unit. The rate of chromosomal inversion substitution is estimated in the origin of the taxon (probably a subgenus of Drosophila rather than a separate genus). It averages no greater than one substitution per 1,000 years, or one per 5,000 generations. The average genetic death rate per generation of one individual per hundred is required to achieve this substitution rate. The rate of inversion substitution during radiation of this taxon may be only 4.4 × 10-3 times as fast as that present in forming the taxon. Alternatively, radiation may have required only 250,000 years if rates of substitution are the same as in the origination of the taxon. Average rates of substitution reflect genetic accidents, selection pressures and rates of adaptation to new niches, as well as the rate of encountering new niches. Rate of adaptation probably is much greater in this instance than rate of encountering new niches. Therefore, the average rate of evolution reflects more nearly biogeographic and ecological factors than genetic factors.
GENETIC VARIATION IN HETEROGENEOUS ENVIRONMENTS
Authors: Taylor Charles E
Published: April 2021

A model of population structure in heterogeneous environments is described and conditions sufficient for maintaining a polymorphism are derived.

The absolute fitness of any genotype is regarded as a function of location in the niche space and the population density at that location. Two modes of habitat selection are examined: (1) organisms are distributed uniformly over the environment; and (2) each organism selects to occupy that habitat in which it is most fit ("optimal habitant selection").—Sufficient conditions for maintenance of genetic polymorphisms are derived for both models. In populations which do not practice habitat selection heterozygote superiority averaged over the environment is sufficient to guarantee the existence of polymorphisms. Comparable conditions for populations which practice optimal habitat selection are much less restrictive. If the heterozygotes are superior to one homozygote in any one part of the niche and to the other homozygote in any other part of the niche then a polymorphism will be defined.—A positive correlation between genetic and environmental variation follows from the model with habitat selection, but not from the other. The adaptive significance of polymorphisms thus depends on how animals behave.