bluuebunny/crossref_metadata_2025 huggingface dataset:
Squeak and Rattle Prevention by Geometric Variation Management Using a Two-Stage Evolutionary Optimization Approach
Authors: Bayani Mohsen , Wickman Casper , Lindkvist Lars , Söderberg Rikard
Published: June 2021

Squeak and rattle are annoying sounds that are often regarded as failure indicators by car users. Geometric variation is a key contributor to the generation of squeak and rattle sounds. Optimization of the connection configuration in assemblies can be a provision to minimize this risk. However, the optimization process for large assemblies can be computationally expensive. The focus of this work is to propose a two-stage evolutionary optimization scheme to find the fittest connection configurations that minimize the risk for squeak and rattle. This was done by defining the objective functions as the measured variation and deviation in the rattle direction and the squeak plane. In the first stage, the location of the fasteners primarily contributing to the rattle direction measures is identified. In the second stage, fasteners primarily contributing to the squeak plane measures are added to the fittest configuration from phase one. It was assumed that the fasteners from the squeak group plane have a lower-order effect on the rattle direction measures, compared to the fasteners from the rattle direction group. This assumption was falsified for a set of simplified geometries. Also, a new uniform space filler algorithm was introduced to efficiently generate an inclusive and feasible starting population for the optimization process by incorporating the problem constraints in the algorithm. For two industrial cases, it was shown that by using the proposed two-stage optimization scheme, the variation and deviation measures in critical interfaces for squeak and rattle improved compared to the baseline results.
Computational and Experimental Analysis of a Compact Combustor Integrated Into a JetCat P90 RXi
Authors: Holobeny Daniel , Bohan Brian T. , Polanka Marc D.
Published: June 2021

Ultra compact combustors (UCCs) look to reduce the overall combustor length and weight in modern gas turbine engines. Previously, a UCC achieved self-sustained operation at subidle speeds in a JetCat P90 RXi turbine engine with a length savings of 33% relative to the stock combustor. However, that combustor experienced flameout as reactions were pushed out of the primary zone before achieving mass flow rates at the engine's idle condition. A new combustor that utilized a bluff body flame stabilization with a larger combustor volume looked to keep reactions in the primary zone within the same axial dimensions. This design was investigated computationally for generalized flow patterns, pressure losses, exit temperature profiles, and reaction distributions at three engine power conditions. The computational results showed the validity of this new UCC, with a turbine inlet temperature of 1080 K and a pattern factor (PF) of 0.67 at the cruise condition. The combustor was then built and tested in the JetCat P90 RXi with rotating turbomachinery and gaseous propane fuel. The combustor maintained a stable flame from ignition through the 36,000 revolutions per minute idle condition. The engine ran self-sustained from 25,000 to 36,000 revolutions per minute with an average exit gas temperature of 980 K, which is comparable to the stock engine.
Influence of Flue Gas Pattern Flow in Boiler Radiant Section on Heat Transfer
Authors: Jaćimović Branislav , Genić Srbislav , Jaćimović Nikola
Published: June 2021

During the sizing of the radiant zone in boilers and furnaces, the most often used method is the Lobo-Evans model. This method is based on the perfect mixing model for flue gas flow inside the fire box, which represents a conservative or pessimistic flow pattern. This paper presents a different, optimistic model which is based on the plug flow for flue gas flow which results in the largest possible heat duty. The proposed model is given in two distinct forms—integral and numerical. As shown in the paper, the integral model results in small deviations with respect to the numerical model and, as such, is well suited for the engineering practice. Paper also presents an engineering approach to the calculation of the conductive heat transfer through the membrane wall, which is shown to be sufficiently accurate and simple for engineering calculations.
Silicon-ion implantation induced doping and nanoporosity in molecular beam epitaxy grown GaSb epitaxial films
Authors: Pandey Rakesh Kumar , Mishra Puspashree , Pandey Akhilesh , Dutta Shankar , Arora Aman , Rath Shyama
Published: June 2021

This paper reports two specific aspects of Si implantation in the molecular beam epitaxy grown p-type GaSb epilayer, namely, the evolution of nanoporosity and doping characteristics. The implantation is done with 100 keV Si ions at four different fluences, i.e., 5 × 1013, 1 × 1014, 5 × 1014, and 1 × 1015 ions/cm2. A field-emission scanning electron microscope (in-plane and cross-sectional view) shows a smooth nanoporous GaSb with a pore diameter of 10–20 nm for the higher fluences. The thickness of the porous film is enhanced from 235 nm (fluence: 1 × 1014 ions/cm2) to 515 nm (fluence: 1 × 1015 ions/ cm2). Development of smooth uniform porous GaSb using Si ion implantation is discussed from the viewpoint of displacement per atom and distribution of vacancies estimated through Stopping and Range of Ions in Matter simulation tool. Hall measurement shows conversion to n-type behavior after implantation and a variation in the sheet carrier concentration from 2.22 × 1014 to 8.52 × 1014 cm−2. There is a drastic change in the mobility with the onset of void formation by implantation.
A management plan for a declining population of the Souss valley tortoise in an arid steppe-land of west-central Morocco
Authors: Nawal Hichami , Znari Mohammed
Published: June 2021

The endangered Moorish tortoise Testudo graeca is the unique terrestrial chelonian species in Northwest Africa. In west-central Morocco, the endemic subspecies, the Souss valley tortoise T. g. soussensis, occupies semi-arid to arid low-quality habitats, and is subject to serious threats. A long-term mark-recapture programme from 2001 to 2012 allowed estimating population size and structure, sex ratio, and survivorship in one of the well-known populations in a degraded and overgrazed arid steppe-land of west-central Morocco. Spring population size considerably decreased to more than half in less than 10 years, with a mean density lower than 3 ind.ha-1 in 2012 compared to its last known density estimated in 2003. In spring 2012, the population structure exhibited an unbalanced male-biased sex ratio (61:39) and a scarcity of juveniles (<5%). We identified five major conservation problems in the study area: (i) habitat destruction and overgrazing; (ii) over-collecting of tortoises for pet trade , iii) direct disturbance; iv) tortoise handling mostly for field research, and v) increased extinction risk due to the small population size. We carried out a population viability analysis using the VORTEX software based on published and obtained data on population and life history parameters. With no management action, the population will go extinct during the forthcoming 40 years after the last estimate. The most efficient management option for a long-term persistence of the population would be reducing the nest and neonate mortality by 90%. To attenuate the impact of the threatening factors, we developed a management plan that includes population reinforcement and habitat restoration options.
The soundscape of quarantine
Authors: Boren Braxton
Published: June 2021

Given the drastic effect of ongoing lockdowns during the COVID-19 pandemic of 2020–2021, many researchers in different fields found themselves learning the basics of epidemiology and public health. However, in the midst of such a crisis, it is incumbent for content experts to apply their own expertise to the problem at hand, no matter how marginal their contribution may be. It is argued that at the broadest level, acousticians may contribute to the mental and physical health of those undergoing pandemic lockdowns via soundscape analysis. Given the widespread lockdown fatigue of staying largely indoors for nearly a year, even small improvements in quality of life under lockdown may be help the wider crisis by helping people follow public health recommendations longer than they otherwise would. The first part of this analysis focuses on noise prevention, especially in multi-unit housing where sound transmission between units can exacerbate social ties. Second, this talk examines the role of acoustic simulation, spatial audio, and VR to open up larger worlds to those under prolonged confinment.
The effect of dose uncertainty on community noise dose-response outcomes
Authors: Horonjeff Richard D.
Published: June 2021

Recent simulations have been performed to determine the effects of dose uncertainty (estimated participant sound levels) on community noise dose-response outcomes. This paper presents a number simulations that illustrate how dose estimation uncertainty, dose range and the frequency distribution of doses across that range combine to modify an underlying true dose-response relationship. It further shows how each combination creates a unique distortion to the underlying curve in the observed results. The complexity of compensating for these uncertainties is discussed, and the paper recommends the formation of standardized data collection practices to enable compensation for them in the analysis.
Prediction of loudness metrics at very high sampling frequencies using digital filters
Authors: Rallabhandi Sriram K.
Published: June 2021

Numerical solution of the augmented Burgers equation is generally the widely used process to predict sonic boom signatures on the ground starting from disturbances generated by an aircraft flying at supersonic speeds. Once the ground waveforms are predicted, loudness metrics are calculated as a means to quantify the impact associated with the underlying sonic booms. This work uses sBOOM, an augmented Burgers equation solver. Within sBOOM, loudness metrics are determined using time-domain digital filters rather than relying on Fast-Fourier Transforms (FFT) and their inverse counterparts to transform back and forth from the frequency-domain. For propagating signals from aircraft concepts that produce extremely low loudness levels, large sampling frequencies may be needed to achieve loudness metric convergence. This work discusses digital filters used within sBOOM, how their accuracy deteriorates at large sampling frequencies, and the enhancements to the digital filter implementation. Additionally, this work will also discuss loudness metric gradients (helpful in aircraft design exercises) obtained using the digital filtering enhancements. Finally, results with and without these modifications, both in terms of loudness metrics and their gradients, will be discussed and presented for cases which may include shaped low-boom as well as strong shock signatures.
Modeling sound-source localization of two sinusoidally amplitude-modulated noises in a sound field
Authors: Pastore M. Torben , Zhou Yi , Yost William A.
Published: June 2021

Yost and Brown [JASA 133 (2013)] investigated the ability of listeners to localize two simultaneously presented, independent noises presented over loudspeakers from different locations. These experiments demonstrated that SAM noises that were out of phase at two spatially separated loudspeakers led to better localization performance than when the SAM noises were in phase at each loudspeaker. Performance was improved at SAM rates as high as almost 500 Hz as compared to non-SAM noise. Yost and Brown hypothesized that listeners’ behavior might be explained as a temporal-spectral (T-S) analysis, and showed that such an approach could, qualitatively, account for some of their behavioral data. This presentation will explore the degree to which a quantitative, biologically inspired peripheral/brainstem auditory model can predict some of the listener performance presented in Yost and Brown 2013. Specifically, the model structure includes simulated auditory nerve response using the Zilany et al. model (JASA, 2014) with rate-count-based estimation of interaural differences of time and intensity as they occur in the presented stimuli recorded with a KEMAR manikin.
Moth wings are acoustic metamaterials
Authors: Neil Thomas R. , Shen Zhiyuan , Robert Daniel , Drinkwater Bruce W. , Holderied Marc W.
Published: June 2021

Intense predation pressure from echolocating bats has led to the evolution of a host of anti-bat defences in nocturnal moths. The wings of moths are covered in scales that exhibit intricate shapes and sculpted nano structures. Here, we reveal that this scale layer forms a metamaterial ultrasound absorber that is 111 times thinner than the longest absorbed wavelength. Both experimental and numerical analyses of individual scale vibrodynamics reveal that the first three resonances of moth scales lie within the typical echolocation frequency range of bats, whilst scale shape diversity on the wing results in a broad resonance distribution. Individual scales form the resonant unit-cells on the wing and collectively they generate hard to attain broadband deep-subwavelength absorption. Numerical modelling confirms that the acoustic properties of moth wings originate from the interaction of differently tuned single scale resonators, creating emergent acoustic performance beyond that of its elements, confirming broadband metamaterial absorber functionality. This sound absorber provides moth wings with acoustic camouflage against echolocating bats, it combines broadband absorption of all frequencies used by bats with light and ultrathin structures that meet aerodynamic constraints on wing weight and thickness.
Numerical simulation of the effect of absorption on the transmission of acoustic waves through 3D-printed ABS-plastic metamaterial
Authors: Korobov Alexander , Kokshaiskiy Alexey , Zhostkov Ruslan A. , Odina Natalia , Izosimova Maria , Volodarsky Alexander
Published: June 2021

When designing acoustic metamaterials, there is often a discrepancy between the calculated sound field and the experimental results. This does not allow you to accomplish the planned purposes, for example, using a metamaterial as a filter in a given frequency range. One of the reasons for this is associated with the effect of losses, which is often not considered. This paper presents the results of numerical simulation of effect of absorption on the acoustic waves propagation in metamaterial elements. Samples in the form of cubes with holes made of 3D-printed ABS-plastic were used as simulation. The attenuation coefficients were taken from the literature and measured in the samples of plastic the metamaterial was made of. Full-wave numerical simulation by the finite element method in the COMSOL Multiphysics software package is performed. Simulation allowed to analyze many different geometries and physical parameters of metamaterial samples and to choose ones with the most designatory properties. The effect of absorption on a number of features, in particular, on the pattern of the bandwidth and reject bands is noted. Numerical and physical experiments are compared. [The research was supported by a grant from the Russian Science Foundation (Project No. 19-12-00098).]
Influence of structural resonances on the causal-based optimisation of micro-perforated absorbers
Authors: Bravo Teresa , Maury Cedric
Published: June 2021

Fire-proofness, cleanability and lightweight constraints make micro-perforated panels an alternative to classical porous materials in demanding environments. However, the selection of their physical parameters constitutes a combinatorial optimization problem that involves the maximization of the absorption coefficient within a frequency band, imposing restrictions on the total thickness of the partition. In this work, we propose an alternative formulation based on the principle of causality. The optimization of micro-perforated absorbers (MPAs) by this criterion enables to identify the MPA constitutive parameters that achieve both critically coupled (CC) resonant states and the smallest thickness-to-bandwidth ratio. It includes the specific resonant state that maximizes the total absorption for a given overall thickness of the absorber. However, the optimization of lightweight absorbers requires that the parameter space involves sub-millimetric panel thicknesses. In this case, the effect of elasticity and finite-sized structural resonances are hardly negligible on the absorption performance. In this study, the causality criterion developed for rigid MPAs has been extended to account for the effect of the panel vibrations on the perforations impedance. Of interest is to examine how this influences the thickness-to-bandwidth performance of the MPA and the related CC resonances, especially when they strongly couple with the cavities Helmholtz-type resonances.
Variability of disyllabic tone 4 sandhi in colloquial Beijing
Authors: Cheng Ruoqian , Zhang Jie
Published: June 2021

This study collects production data remotely from speakers of colloquial Beijing in China. Acoustic analysis is conducted to test the surface variation of an underlying falling tone between falling and rising when preceding another underlying fall tone.
Tips for interviewing people with hearing loss over Zoom
Authors: Pearson Madison , Freeman Valerie L.
Published: June 2021

This presentation will cover considerations for effectively conducting interviews or other interactive experiments over Zoom with individuals who have hearing loss, with or without assistive listening devices, closed captioning, interpreters, or other accommodations.
Socially distanced psychoacoustics
Authors: Wilson Vayda , Balant Anne C. , Lai Heather L.
Published: June 2021

This presentation will describe the successful adaptation of a psychoacoustic study on acoustic analogs of flutter echoes for remote participation. The data collection software was installed on a campus server and the investigators guided the participants through three different listening tasks via screen-sharing and videoconferencing.
Incidence of data augmentation in machine learning using broadband spectrograms
Authors: Castro-Correa Jhon A. , Badiey Mohsen , Neilsen Tracianne B. , Knobles David P.
Published: June 2021

One of the main problems in ocean acoustics is the lack of training data that assist networks to generalize better understand undersea environments. In deep learning, data augmentation is commonly used to add variability to the data by applying small transformations to the samples with the purpose of improving the performance and generalization capabilities of the networks. Here, this definition is extended to broadband spectrograms from merchant ships collected during the Seabed Characterization Experiment in 2017. In this study, residual neural networks were used as the machine learning algorithm for performing source localization and environment classification. Additionally, nine different data augmentation techniques were considered for studying their performance predictions. Each of the transformations was applied to the data set during the training stage, and the results were compared to establish the effects in the performance for both regression and classification tasks. The metrics used were the root mean squared error for regression and accuracy in the case of seabed classification. The results show a favorable potential of residual-based deep learning models to differentiate the seabed types and the source position based on these types of data, in addition to the improvements in performance after applying complex transformations during the training. [Work supported by the Office of Naval Research, Contract No. N00014-19-C-2001.]
Automated detection of liver steatosis in ultrasound images using convolutional neural networks
Authors: Mohammmad Umar Farooq , Almekkawy Mohamed
Published: June 2021

Ultrasound imaging is the most commonly applied imaging modality for the diagnosis of fatty liver disease. It is considered malignant if there is more than 5% of fatty hepatorenal steatosis. The classical methods to classify liver steatosis usually involve experienced physicians or radiologists to identity them. In this work, we introduce a Convolutional Neural Network (CNN) based approach to classify the malignant and benign fatty livers from ultrasound images. The pre-trained network of Inception Resnet which is initially trained on the ImageNet dataset is used for transfer learning on B-mode ultrasound liver images for classification. We used the open-source ultrasound liver dataset of 55 patients with 10 image sequences for each making a total of 550 images with 170 benign and 340 malignant samples. Since the dataset size is small for training, we have applied various data-augmentation techniques and have employed the transfer-learning approach using Inception ResNet architecture. We were able to achieve, using our approach, a very high classification accuracy of 98.48%, whereas the area under the curve of the classical hepatorenal index method is 0.959 and the Gray-level co-occurrence algorithm is 0.893.
Acoustic characterization and stability assessment of size-isolatedprotein-shelled microbubbles
Authors: Suresh Boyapati , Khan Aaqib , Shah Dipesh , Dalvi Sameer V. , Shah Himanshu Shekhar
Published: June 2021

The side size distribution of ultrasound contrast agents has a strong effect on their performance in therapy and imaging. In this work, attenuation spectroscopy was performed to characterize the acoustic response and stability of three size-isolated populations of protein-shelled microbubbles with mean diameters ranging from 1.66 to 3.77 μm.
The influence of echogenic liposome bubble nuclei on histotripsy cavitation dynamics
Authors: Bhargava Aarushi , Huang Shaoling , McPherson David D. , Bader Kenneth B.
Published: June 2021

Histotripsy is a focused ultrasound therapy under development for thrombus ablation through bubble cloud nucleation, and combining it with a thrombolytic-loaded theragnostic agent will expand its treatment capacity. In this study, echogenic liposomes encapsulating a lytic were exposed to histotripsy pulses, and the resulting bubble dynamics were examined with passive and active imaging.
Static magnetic fields dampen focused ultrasound-mediated blood-brain barrier opening
Authors: Yang Yaoheng , Pham Pacia Christopher , Ye Dezhuang , Yue Yimei , Chien Chih-Yen , Chen Hong
Published: June 2021

The static magnetic field of an MRI scanner was found to dampen the microbubble cavitation activity and decrease the focused ultrasound-combined with microbubble-mediated blood-brain barrier opening.
Evolution of some newer flextensional transducer designs
Authors: Butler John , Curtis Victoria
Published: June 2021

Flextensional transducers, such as the classic oval Class IV, have provided a means for magnified high output at low frequencies from a small size, when compared with Tonpilz piston transducers. We present here a transition to other newer flextensional types and shapes, such as the cylindrical Trioid and LCAT transducers and the piston cantilever mode transducer, CMX. We will show that these transitions came about after a flextensional X-spring design was realized. Although the X-spring was originally conceived to increase the output and also lower the resonance frequency of Tonpilz piston transducers, it also turned out to provide a significant means for the development of newer flextensional transducer designs. Examples of these newer designs and their operation, as well as an initially unexpected improved lower frequency performance from an array of CMX transducers, will be presented. [Work supported in part by Office of Naval Research.]
Personal audio system use can harm auditory health
Authors: Mayes Jan L. , Fink Daniel
Published: June 2021

Personal audio systems (PAS) are a major source of harmful noise doses, especially for children, teenagers, and young adults, who typically listen many hours daily at volumes exceeding the globally recommended public health limit of 70 dBA LEQ24h. PAS users increase listening volume to overcome high ambient noise. Research shows that (1) PAS use among people aged 9 + is associated with permanent, progressive hearing health disabilities including tinnitus, hyperacusis, speech communication impairments, and noise-induced hearing loss (NIHL); i(2) auditory health risk is highest for personal listening 1 + hours daily at over 50% volume with 5 + years of exposure; (3) clinical measures demonstrate noise-induced neural or retrocochlear auditory processing disorders precede sensory or cochlear impairments; and (4) children are highest risk because auditory system maturation is incomplete and normal hearing health is vital for learning, socialization, and vocational potential. Acquired hearing loss is associated with increased risk of accidents, communication difficulties, social isolation, and health impairments, including dementia in later life. Public health hearing conservation policies are needed to prevent an imminent NIHL epidemic in younger generations, including PAS noise emission standards and public education on the dangers of PAS use and about safer listening behaviors.
Spectral envelope position and shape in sustained musical instrument sounds
Authors: Siedenburg Kai , Jacobsen Simon , Reuter Christoph
Published: June 2021

It has been argued that the relative position of spectral envelopes along the frequency axis serves as a cue for musical instrument size (e.g., violin vs viola) and that the shape of the spectral envelope encodes family identity (violin vs flute). It is further known that fundamental frequency (F0), F0-register for specific instruments, and dynamic level strongly affect spectral properties of acoustical instrument sounds. However, the associations between these factors have not been rigorously quantified for a representative set of musical instruments. Here, we analyzed 5640 sounds from 50 sustained orchestral instruments sampled across their entire range of F0s at three dynamic levels. Regression of spectral centroid (SC) values that index envelope position indicated that smaller instruments possessed higher SC values for a majority of instrument classes (families), but SC also correlated with F0 and was strongly and consistently affected by the dynamic level. Instrument classification using relatively low-dimensional cepstral audio descriptors allowed for discrimination between instrument classes with accuracies beyond 80%. Envelope shape became much less indicative of instrument class whenever the classification problem involved generalization to different dynamic levels or F0-registers. These analyses confirm that spectral envelopes encode information about instrument size and family identity and highlight their dependence on F0(-register) and dynamic level.
Repression of penicillin G acylase of Proteus rettgeri by tricarboxylic acid cycle intermediates
Authors: Daumy G O , McColl A S , Apostolakos D
Published: June 2021

The regulation of the penicillin acylase in proteus rettgeri ATCC 31052 was compared with that of the enzyme in Escherichia coli ATCC 9637. Unlike the E. coli acylase, the P. rettgeri enzyme was not induced by phenylacetic acid, nor was it subject to catabolite repression by glucose. The P. rettgeri acylase appears to be expressed constitutively but is subject to repression by the C4-dicarboxylic acids of the tricarboxylic acid cycle, succinate, fumarate, and malate.
Insertion of a MalE β-Galactosidase Fusion Protein into the Envelope of
Escherichia coli
Disrupts Biogenesis of Outer Membrane Proteins and Processing of Inner Membrane Proteins
Authors: Herrero Enrique , Jackson Maria , Bassford Phillip J. , Sinden David , Holland I. Barry
Published: June 2021

The synthesis of a membrane-bound MalE β-galactosidase hybrid protein, when induced by growth of
Escherichia coli
on maltose, leads to inhibition of cell division and eventually a reduced rate of mass increase. In addition, the relative rate of synthesis of outer membrane proteins, but not that of inner membrane proteins, was reduced by about 50%. Kinetic experiments demonstrated that this reduction coincided with the period of maximum synthesis of the hybrid protein (and another maltose-inducible protein, LamB). The accumulation of this abnormal protein in the envelope therefore appeared specifically to inhibit the synthesis, the assembly of outer membrane proteins, or both, indicating that the hybrid protein blocks some export site or causes the sequestration of some limiting factor(s) involved in the export process. Since the MalE protein is normally located in the periplasm, the results also suggest that the synthesis of periplasmic and outer membrane proteins may involve some steps in common. The reduced rate of synthesis of outer membrane proteins was also accompanied by the accumulation in the envelope of at least one outer membrane protein and at least two inner membrane proteins as higher-molecular-weight forms, indicating that processing (removal of the N-terminal signal sequence) was also disrupted by the presence of the hybrid protein. These results may indicate that the assembly of these membrane proteins is blocked at a relatively late step rather than at the level of primary recognition of some site by the signal sequence. In addition, the results suggest that some step common to the biogenesis of quite different kinds of envelope protein is blocked by the presence of the hybrid protein.
Regulation of invertase synthesis by glucose in Saccharomyces cerevisiae
Authors: Mormeneo S , Sentandreu R
Published: June 2021

Saccharomyces cerevisiae growing under repressible conditions (1% of glucose or more) produces a burst of external invertase when shifted to higher temperatures. The secretion of this invertase requires protein synthesis, but was found to be independent of RNA formation. The level of mRNA accumulated and translated was inversely proportional to the glucose present in the growth medium. These results are consistent with the hypothesis that invertase is continuously synthesized both in the presence and absence of glucose, but under repressible conditions is degraded before secretion takes place.
Transformation-deficient mutants of Bacillus subtilis impaired in competence-specific nuclease activities
Authors: Mulder J A , Venema G
Published: June 2021

A comparison of the nucleolytic activities in competent and physiologically low-competent wild-type cultures of Bacillus subtilis in DNA-containing sodium dodecyl sulfate-polyacrylamide gels revealed the existence of three competence-associated nuclease activities with apparent molecular weights of 13,000, 15,000, and 26,000. The three activities, which were dependent on manganese or magnesium ions, were specifically present in the competent fraction of a competent culture. The competence-associated nucleolytic activities of eight transformation-defective mutant strains were assayed, resulting in the following three classes of mutants: (i) four strains which, according to this assay, were not impaired in any of the nucleolytic activities mentioned above; (ii) one strain which was strongly impaired in the 13,000- and 26,000-molecular-weight activities, but showed a considerable level of the 15,000-molecular-weight activity; and (iii) three strains which were severely impaired in all three activities. The results indicated that the 26,000-molecular-weight activity was a dimer of the 13,000-molecular-weight activity and that this nuclease was involved in the entry of DNA.
Transformation of restriction endonuclease phenotype in Streptococcus pneumoniae
Authors: Muckerman C C , Springhorn S S , Greenberg B , Lacks S A
Published: June 2021

The genetic basis of the unique restriction endonuclease DpnI, that cleaves only at a methylated sequence, 5'-GmeATC-3', and of the complementary endonuclease DpnII, which cleaves at the same sequence when it is not methylated, was investigated. Different strains of Streptococcus pneumoniae isolated from patients contained either DpnI (two isolates) or DpnII (six isolates). The latter strains also contained DNA methylated at the 5'-GATC-3' sequence. A restrictable bacteriophage, HB-3, was used to characterize the various strains and to select for transformants. One laboratory strain contained neither DpnI nor Dpn II. It was probably derived from a DpnI-containing strain, and its DNA was not methylated at 5'-GATC-3'. Cells of this strain were transformed to the DpnI restriction phenotype by DNA from a DpnI-containing strain and to the DpnII restriction phenotype by DNA from a DpnII-containing strain. Neither cross-transformation, that is, transformation to one phenotype by DNA from a strain of the other phenotype, nor spontaneous conversion was observed. Extracts of transformants to the new restriction phenotype were shown to contain the corresponding endonuclease.
Regulation of the ColV plasmid-determined iron (III)-aerobactin transport system in Escherichia coli
Authors: Braun V , Burkhardt R
Published: June 2021

Regulation by iron was studied in Escherichia coli strains whose iron supply was entirely dependent on the iron(III)-aerobactin system determined by the ColV plasmid. By the insertion of phage Mu (Ap lac) into the ColV plasmid, mutants were selected that could no longer grow in iron-limited media. The inserted Mu (Ap lac) strongly reduced the amount of aerobactin and he cloacin receptor protein formed by the cells. Their production was no longer subject to regulation by iron. The Mu (Ap lac) insertion apparently led to a polar effect on the expression of the presumably closely linked genes that control the synthesis of aerobactin and the cloacin receptor protein. The expression of the beta-galactosidase gene on the inserted phage genome came under the control of the iron state of the cells. Under iron-limited growth conditions, the amount of beta-galactosidase synthesized was, depending on the strain studied, 6 to 30 times higher than under iron-sufficient growth conditions. In fur mutants with an impaired iron regulation of ll iron supply systems studied so far, high amounts of beta-galactosidase were synthesized independent of the cells' iron supply. The results demonstrate an iron-controlled promoter on the ColV plasmid which is subject to regulation by the chromosomal fur gene.
Genetic mapping of mutations in a highly radiation-resistant mutant of Salmonella typhimurium LT2
Authors: Ibe S N , Sinskey A J , Botstein D
Published: June 2021

The genes involved in the high radiation resistance of mutant R68 of Salmonella typhimurium LT2 were mapped by conjugation. It was observed that the high radiation resistance involved genes localized in two regions of the chromosome, which have been designated as garA and garB for high gamma resistance. The garA gene mapped near gal and uvrB at about 18 map units, and the garB gene mapped near purC at about 49 map units. The resistance of R68 was reduced to the wild-type level by the acquisition of the two wild-type alleles, garA+ and garB+. Recombinants carrying the garA or garB gene repaired single-strand breaks in their DNA faster than did the wild-type strain. However, only those with the garA mutation showed a marked increase in UV irradiation resistance above the wild-type level, whereas those with garB mutation exhibited an increased rate of spontaneous degradation of DNA beyond the level observed in recA cells.
Interference of plasmid pCM194 with lysogeny of bacteriophage SP02 in Bacillus subtilis
Authors: Marrero R , Lovett P S
Published: June 2021

Three observations indicated that the 2-megadalton chloramphenicol resistance plasmid pCM194 interferes with SP02 lysogeny of Bacillus subtilis. SP02 plaques formed on B. subtilis(pCM194) appeared almost clear, whereas plaques produced on plasmid-free or pUB110-containing cells contained large turbid centers. The number of phages spontaneously liberated by B. subtilis(SP02) was increased 10-fold or more when pCM194 was also present in the lysogens. Lastly, growth of B. subtilis(SP02, pCM194) for approximately 20 to 25 generations resulted in essentially complete loss of the prophage. This interference was not observed with pUB110 or pE194, and the pCM194 interference was not directed against B. subtilis temperate phage phi 105, which is unrelated to SP02. Lytic replication of SP02 appeared to be unaffected by pCM194. pCM194 interference with SP02 lysogeny was demonstrable in recombination-proficient strains and a recE mutant of B. subtilis. SP02 prophage which were noninducible due to the phage ind mutation were resistant to pCM194 interference. pCM194 interference was lost when the entire pCM194 molecule was joined at its unique HpaII site or at one of the two MboI sites to pUB110 or pUB110 derivatives. pBR322 joined to pCM194 at the same MboI site or at the HindIII site produced chimeras that retained the ability to interfere with SP02 lysogeny. A three-part plasmid constructed by joining pBR322 to pCM194 (at HindIII sites) and to pE194 (at PstI sites) was compatible with the SP02 prophage and showed a temperature-sensitive replication phenotype characteristic of the pE194 replicon. One explanation for the interference involves competition for a host component between an SP02 genome attempting to establish lysogeny and plasmids whose replication is directed by the pCM194 replicon.
Extraction and properties of hemagglutinin from cell wall fragments of Fusobacterium nucleatum
Authors: Dehazya P , Coles R S
Published: June 2021

To study the hemagglutinin of Fusobacterium nucleatum, methods were sought to solubilize and purify this component. When cells of F. nucleatum were ruptured by passage through a French press, the fragments lost virtually all ability to agglutinate human erythrocytes. Extraction of the fragments with 2% Triton X-100 for 30 min at 22 degrees C restored hemagglutinating activity (HA). Hemagglutination by these fragments could be inhibited by arginine, as can hemagglutination by intact bacteria. Treatment of active cell wall fragments with pronase and 2% Triton X-100-EDTA at 37 degrees C or with pronase and 0.1% Triton X-100-EDTA at pH 10.0 allowed recovery of solubilized HA. The former HA was inhibited by arginine (arg+) whereas the latter was not (arg-). Fractionation of the arg+ extract by preparative isoelectric focusing showed that HA was recovered from the gel sections having a pH between 4.5 and 5.5. Hemagglutination by this preparation was still arg+. Chromatography of this hemagglutinin on DEAE-Sephadex increased the specific activity to high levels with a loss of inhibition by arginine. A fraction from the DEAE-Sephadex column containing 10,700 HA units per mg of protein was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Solubilization at 22 degrees C before electrophoresis revealed three Coomassie blue-staining bands which migrated with apparent molecular weights of about 21,000, 38,000 and 60,000. When the same DEAE fraction was boiled in sodium dodecyl sulfate, electrophoresis revealed only one band with an apparent molecular weight of 21,000.
Antagonism of the B subunit of DNA gyrase eliminates plasmids pBR322 and pMG110 from Escherichia coli
Authors: Wolfson J S , Hooper D C , Swartz M N , McHugh G L
Published: June 2021

The constructed plasmid pBR322 and the native plasmid pMG110 were eliminated (cured) from growing Escherichia coli cells by the antagonism of the B subunit of the bacterial enzyme DNA gyrase. The antagonism may be by the growth of cells (i) at semipermissive temperatures in a bacterial mutant containing a thermolabile gyrase B subunit or (ii) at semipermissive concentrations of coumermycin A1, an antibiotic that specifically inhibits the B subunit of DNA gyrase. The kinetics of plasmid elimination indicate that plasmid loss occurs too rapidly to be explained solely by the faster growth of that plasmid-free bacteria and, therefore, represents interference with plasmid maintenance.
Recombination properties of P1 dlac
Authors: Porter R D
Published: June 2021

The P1 dlac prophage plasmid of Escherichia coli K-12 has been utilized as the recipient DNA substrate in experiments with lambda plac5 transduction and with Hfr and F' conjugation. The P1 dlac plasmid does not recombine with lambda plac5 at the elevated levels seen for the F42lac plasmid. Recombination between lambda plac5 and P1 dlac is essentially indistinguishable from recombination between lambda plac5 and a chromosomal lac gene in tems of both level of recombination and recombination pathway (RecBC, RecE, and RecF) dependence. The initiation of recombination between P1 dlac and lac genes from an Hfr or F' donor is severalfold more efficient than it is for a recipient chromosomal lac gene.
Regulatory region of the Klebsiella aerogenes tryptophan operon
Authors: Blumenberg M , Yanofsky C
Published: June 2021

The trp operon of Klebsiella aerogenes was cloned, and its regulatory region was sequenced. Comparison with previously reported trp regulatory sequences of other enteric bacteria indicates that the K. aerogenes trp promoter-operator region is most similar to the corresponding region of Salmonella typhimurium. The trp leader regions of K. aerogenes and other enteric bacteria are organized similarly, but there are significant differences in the stabilities of the predicted secondary structures in their leader transcripts. These differences should make the K. aerogenes attenuator a weaker transcription termination site than any of the other attenuator regions studied; this was confirmed in in vitro transcription experiments. The sequence of the leader transcript and the precise site of in vitro termination were determined.
Genetic transformation of Rhodopseudomonas sphaeroides by plasmid DNA
Authors: Fornari C S , Kaplan S
Published: June 2021

A broad-host-range cloning vector, pUI81, was constructed in vitro from plasmids RSF1010 and pSL25 (a pBR322 derivative) and used to assay for transformation in Rhodopseudomonas sphaeroides. Washing cells with 500 mM Tris was an effective means of inducing competence for DNA uptake. Transformation frequencies as high as 10(-5) (transformants per viable cell) have been achieved by incubating Tris-treated cells with plasmid DNA, 100 mM CaCl2, and 20% polyethylene glycol 6000. Maximum frequencies were obtained when recipient cells were spread onto selective media after a 6.5-h outgrowth period in antibiotic-free medium. The structure (open circular versus closed, covalent circular), size, and concentration of plasmid DNA all significantly affected the transformation frequency. Four different plasmids, all small and suitable as cloning vectors, have been introduced by transformation into several different R. sphaeroides strains. Recombinant DNA carried on small, nonconjugative plasmids with broad host ranges can now be directly transferred to R. sphaeroides by this method.
Replication and incompatibility properties of plasmid pE194 in Bacillus subtilis
Authors: Gryczan T J , Hahn J , Contente S , Dubnau D
Published: June 2021

pE194, a 3.5-kilobase multicopy plasmid, confers resistance to the macrolide-lincosamide-streptogramin B antibiotics in Bacillus subtilis. By molecular cloning and deletion analysis we have identified a replication segment on the physical map of this plasmid, which consists of about 900 to 1,000 base pairs. This segment contains the replication origin. It also specifies a trans-acting function (rep) required for the stable replication of pE194 and a negatively acting copy control function which is the product of the cop gene. The target sites for the rep and cop gene products are also within this region. Two incompatibility determinants have been mapped on the pE194 genome and their properties are described. One (incA) resides within the replication region and may be identical to cop. incB, not located in the replication region, expresses incompatibility toward a copy control mutant (cop-6) but not toward the wild-type replicon.
Biosynthesis of oxygen-detoxifying enzymes in Bdellovibrio stolpii
Authors: Von Stein R S , Barber L E , Hassan H M
Published: June 2021

Axenically grown Bdellovibrio stolpii (i.e., grown independently of the host) was examined for superoxide dismutase, catalase, and peroxidase activities. Kinetics of enzyme synthesis were determined for aerobically grown cultures and for cultures exposed to 100% oxygen. Enzymatic activities varied with the age of the culture. Normally grown cultures exhibited maximum activity during the first 10 h of growth and again as the stationary phase was approached, beginning at about 48 h. Polyacrylamide gel electropherograms of cell-free extracts revealed that B. stolpii contained one major band (1) and two minor bands (II, III) of superoxide dismutase activity. Each of these enzymes was inactivated by H2O2, indicating that they were iron-containing enzymes. Manganese-containing superoxide dismutase was not detected in B. stolpii. Increased oxygenation did not appreciably stimulate enzyme synthesis, for only superoxide dismutase was induced, reaching maximum activity at 10 h and then rapidly falling to normal levels. Superoxide dismutase appears to be the main enzymatic defense against oxygen toxicity in B. stolpii. Induction of superoxide dismutase with 100% oxygen was manifested as an increase in the intensities of the two minor bands of activity, suggesting that isozyme I is constitutive, whereas isozymes II and III are inducible. The induction of isozymes II and III by 100% oxygen was prevented by an inhibitor of protein biosynthesis, chloramphenicol.
Genetics and regulation of peptidase N in Escherichia coli K-12
Authors: McCaman M T , McPartland A , Villarejo M R
Published: June 2021

Escherichia coli K-12 strains contain a cytoplasmic activity, peptidase N, capable of hydrolyzing alanine-p-nitroanilide. Mutations in the structural gene for the enzyme, pepN, were mapped, and the properties of mutant strains were examined. The pepN locus lay between ompF and asnS at approximately 20.8 min on the E. coli chromosome. Loss of peptidase N activity through mutation had no apparent effect on the growth rate or nutritional needs of the cell. Enzyme levels in wild-type strains were constant throughout the growth cycle and were constitutive in all of the growth media tested. Starvation for carbon, nitrogen, or phosphate also did not alter enzyme levels. Constitutive expression of peptidase N is consistent with the idea that the enzyme plays a significant role in the degradation of intracellularly generated peptides.
Ornithine-Containing Lipid of
Bordetella pertussis
That Carries Hemagglutinating Activity
Authors: Kawai Yohko , Moribayashi Atsuko , Yano Ikuya
Published: June 2021

The proposed structure of the ornithine-containing lipid of
Bordetella pertussis
is 3-hydroxyhexadecanoic acid amide-linked to ornithine and esterified to the second hexadecanoic acid. The aminolipid strongly agglutinates type A and B human erythrocytes.
Pyruvate oxidation by the Reiter strain of Treponema phagedenis
Authors: George H A , Smibert R M
Published: June 2021

Spectrophotometric assays of pyruvate oxidation catalyzed by extracts of the Reiter strain of Treponema phagedenis indicated that viologen dyes, flavin nucleotides, and a ferric iron chelate, but not pyridine nucleotides, were utilized as electron acceptors. Benzyl viologen-linked activity partially sedimented during ultracentrifugation and appeared similar to clostridial pyruvate:ferredoxin oxidoreductase with respect to the spectral properties of the enzyme chromophore. Electron carrier activity in treponemal extracts was quantitated by a metronidazole-linked assay in which the oxidation of pyruvate by carrier-depleted extracts led to the reduction of electron carrier in the crude extracts which then reduced metronidazole. The rate of metronidazole reduction was proportional to the amount of electron carrier present in the assay. Electron carrier activity in Triton X-100-solubilized, crude extracts partially purified by DEAE-cellulose chromatography and gel filtration was attributed to a protein possessing the spectral and physical properties of a ferredoxin. A similar protein appeared to be present in extracts of Treponema denticola ST10.