Sound Emissions by a Laboratory Bubble Cloud

This paper presents the results obtained from a detailed study of the sound field within and around a cylindrical column of bubbles generated at the center of an experimental water tank. The bubbles were produced by forcing air through a circular array of hypodermic needles. As they separated from the needles the ‘‘birthing wails’’ produced were found to excite the column into normal modes of oscillation whose spatial pressure?amplitude distribution could be tracked in the vertical and horizontal directions. The frequencies of vibration were predicted from theoretical calculations based on a collective oscillation model and showed close agreement with the experimentally measured values. On the basis of a model of the column excitation, absolute sound levels were analytically calculated with results again in agreement with the measured values. These findings provide considerable new evidence to support the notion that bubble plumes can be a major source of underwater sound around frequencies of a few hundred hertz

Kinetochore assembly and heterochromatin formation occur autonomously in Schizosaccharomyces pombe

Kinetochores in multicellular eukaryotes are usually associated with heterochromatin. Whether this heterochromatin simply promotes the cohesion necessary for accurate chromosome segregation at cell division or whether it also has a role in kinetochore assembly is unclear. Schizosaccharomyces pombe is an important experimental system for investigating centromere function, but all of the previous work with this species has exploited a single strain or its derivatives. The laboratory strain and most other S. pombe strains contain three chromosomes, but one recently discovered strain, CBS 2777, contains four. We show that the genome of CBS 2777 is related to that of the laboratory strain by a complex chromosome rearrangement. As a result, two of the kinetochores in CBS 2777 contain the central core sequences present in the laboratory strain centromeres, but lack adjacent heterochromatin. The closest block of heterochromatin to these rearranged kinetochores is ∼100 kb away at new telomeres. Despite lacking large amounts of adjacent heterochromatin, the rearranged kinetochores bind CENP-ACnp1 and CENP-CCnp3 in similar quantities and with similar specificities as those of the laboratory strain. The simplest interpretation of this result is that constitutive kinetochore assembly and heterochromatin formation occur autonomously

Developing evidence-based resources for evaluating postgraduate trainees in the biomedical sciences

Postgraduate trainees elevate the academic strength of institutions by conducting research, promoting innovation, securing grant funding, training undergraduate students, and building alliances. Rigorous and systematic program evaluation can help ensure that postgraduate training programs are achieving the program’s intended outcomes. The purpose of this project was to develop evidence-based evaluation tools that could be shared across federally funded biomedical training programs to enhance program evaluation capacity. This manuscript describes the evidence-based process used to determine program evaluation needs of these programs at a research-intensive university. Using a multi-phased sequential exploratory mixed methods approach, data were collected from trainees, employers, leaders, and program directors. Data analyses included document analysis of program plans, inductive coding of focus groups and interviews, and descriptive analysis of surveys. Two overarching categories–Trainee Skills and Program Characteristics—were identified including six themes each. Program directors prioritized communication, social and behavioral skills, and collaboration as the trainee skills that they needed the most help evaluating. Furthermore, program directors prioritized the following program characteristics as those that they needed the most help evaluating: training environment, trainee outcomes, and opportunities offered. Surveys, interview scripts, and related resources for the categories and themes were developed and curated on a publicly available website for program directors to use in their program evaluations

Magnetization of a two-dimensional electron gas with a second filled subband

We have measured the magnetization of a dual-subband two-dimensional electron gas, confined in a GaAs/AlGaAs heterojunction. In contrast to two-dimensional electron gases with a single subband, we observe non-1/B-periodic, triangularly shaped oscillations of the magnetization with an amplitude significantly less than $1 \mu_{\mathrm{B}}^*$ per electron. All three effects are explained by a field dependent self-consistent model, demonstrating the shape of the magnetization is dominated by oscillations in the confining potential. Additionally, at 1 K, we observe small oscillations at magnetic fields where Landau-levels of the two different subbands cross.Comment: 4 pages, 4 figure

Collisions of Cosmic F- and D-strings

Recent work suggests that fundamental and Dirichlet strings, and their (p,q) bound states, may be observed as cosmic strings. The evolution of cosmic string networks, and therefore their observational signals, depends on what happens when two strings collide. We study this in string perturbation theory for collisions between all possible pairs of strings; different cases involve sphere, disk, and annulus amplitudes. The result also depends on the details of compactification; the dependence on ratios of scales is only logarithmic, but this is still numerically important. We study a range of models and parameters, and find that in most cases these strings can be distinguished from cosmic strings that arise as gauge theory solitons.Comment: 42 pages, 7 figures; v.2: added references, expanded discussion of reconnection in field theor

Ratios of Elastic Scattering of Pions from 3H and 3He

We have measured the elastic-scattering ratios of normalized yields for charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we completed the angular distribution begun with our earlier measurements, adding six data points in the angular range of 119 deg to 169 deg in the pi-nucleus center of mass. We also measured an excitation function with data points at 142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle for each energy between 160 deg and 170 deg in the pi-nucleus center of mass. This excitation function corresponds to the energies of our forward-hemisphere studies. The data, taken as a whole, show an apparent role reversal of the two charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data > 100 deg we observe a strong dependence on the four-momentum transfer squared (-t) for all of the ratios regardless of pion energy or scattering angle, and we find that the superratio R data match very well with calculations based on the forward-hemisphere data that predicts the value of the difference between the even-nucleon radii of 3H and 3He. Comparisons are also made with recent calculations incorporating different wave functions and double scattering models.Comment: RevTex 8pages, 12 figure file

Commensal Neisseria species share immune suppressive mechanisms with Neisseria gonorrhoeae

Neisseria gonorrhoeae is a highly adapted human sexually transmitted pathogen that can cause symptomatic infections associated with localized inflammation as well as asymptomatic and subclinical infections, particularly in females. Gonococcal infection in humans does not generate an effective immune response in most cases, which contributes to both transmission of the pathogen and reinfection after treatment. Neisseria gonorrhoeae is known to evade and suppress human immune responses through a variety of mechanisms. Commensal Neisseria species that are closely related to N. gonorrhoeae, such as N. cinerea, N. lactamica, N. elongata, and N. mucosa, rarely cause disease and instead asymptomatically colonize mucosal sites for prolonged periods of time without evoking clearing immunologic responses. We have shown previously that N. gonorrhoeae inhibits the capacity of antigen-pulsed dendritic cells to induce CD4+ T cell proliferation in vitro. Much of the suppressive effects of N. gonorrhoeae on dendritic cells can be recapitulated either by outer-membrane vesicles released from the bacteria or by purified PorB, the most abundant outer-membrane protein in Neisseria gonorrhoeae. We show here that three commensal Neisseria species, N. cinerea, N. lactamica and N. mucosa, show a comparable capacity to suppress dendritic cell-induced T cell proliferation in vitro through mechanisms similar to those demonstrated previously for N. gonorrhoeae, including inhibition by purified PorB. Our findings suggest that some immune-evasive properties of pathogenic N. gonorrhoeae are shared with commensal Neisseria species and may contribute to the ability of both pathogens and commensals to cause prolonged mucosal colonization in humans

Semiclassical Theory of Coulomb Blockade Peak Heights in Chaotic Quantum Dots

We develop a semiclassical theory of Coulomb blockade peak heights in chaotic quantum dots. Using Berry's conjecture, we calculate the peak height distributions and the correlation functions. We demonstrate that the corrections to the corresponding results of the standard statistical theory are non-universal and can be expressed in terms of the classical periodic orbits of the dot that are well coupled to the leads. The main effect is an oscillatory dependence of the peak heights on any parameter which is varied; it is substantial for both symmetric and asymmetric lead placement. Surprisingly, these dynamical effects do not influence the full distribution of peak heights, but are clearly seen in the correlation function or power spectrum. For non-zero temperature, the correlation function obtained theoretically is in good agreement with that measured experimentally.Comment: 5 color eps figure

P2Y1 receptor modulation of endogenous ion channel function in Xenopus oocytes: Involvement of transmembrane domains

Agonist activation of the hP2Y1 receptor expressed in Xenopus oocytes stimulated an endogenous voltage-gated ion channel, previously identified as the transient inward (Tin) channel. When human P2Y1 (hP2Y1) and skate P2Y (sP2Y) receptors were expressed in Xenopus oocytes, time-to-peak values (a measure of the response to membrane hyperpolarization) of the Tin channel were significantly reduced compared to oocytes expressing the hB1-bradykinin receptor or the rat M1-muscarinic (rM1) receptor. Differences in activation were also observed in the Tin currents elicited by various P2Y receptor subtypes. The time-to-peak values of the Tin channel in oocytes expressing the hP2Y4, hP2Y11, or hB1-bradykinin receptors were similar, whereas the channel had significantly shorter time-to-peak values in oocytes expressing either the hP2Y1 or sP2Y receptor. Amino acid substitutions at His-132, located in the third transmembrane domain (TM3) of the hP2Y1 receptor, delayed the onset of channel opening, but not the kinetics of the activation process. In addition, Zn2+ sensitivity was also dependent on the subtype of P2Y receptor expressed. Replacement of His-132 in the hP2Y1 receptor with either Ala or Phe increased Zn2+ sensitivity of the Tin current. In contrast, truncation of the C-terminal region of the hP2Y1 receptor had no affect on activation or Zn2+ sensitivity of the Tin channel. These results suggested that TM3 in the hP2Y1 receptor was involved in modulating ion channel function and blocker pharmacology of the Tin channel