Sensitivity to interaural time differences in the medial superior olive of a small mammal, the Mexican free-tailed bat

Neurons in the medial superior olive (MSO) are thought to encode interaural time differences (ITDs), the main binaural cues used for localizing low-frequency sounds in the horizontal plane. The underlying mechanism is supposed to rely on a coincidence of excitatory inputs from the two ears that are phase-locked to either the stimulus frequency or the stimulus envelope. Extracellular recordings from MSO neurons in several mammals conform with this theory. However, there are two aspects that remain puzzling. The first concerns the role of the MSO in small mammals that have relatively poor low-frequency hearing and whose heads generate only very small ITDs. The second puzzling aspect of the scenario concerns the role of the prominent binaural inhibitory inputs to MSO neurons. We examined these two unresolved issues by recording from MSO cells in the Mexican free-tailed bat. Using sinusoidally amplitude-modulated tones, we found that the ITD sensitivities of many MSO cells in the bat were remarkably similar to those reported for larger mammals. Our data also indicate an important role for inhibition in sharpening ITD sensitivity and increasing the dynamic range of ITD functions. A simple model of ITD coding based on the timing of multiple inputs is proposed. Additionally, our data suggest that ITD coding is a by-product of a neuronal circuit that processes the temporal structure of sounds. Because of the free-tailed bat's small head size, ITD coding is most likely not the major function of the MSO in this small mammal and probably other small mammals

Efficiency of surface-driven motion: nano-swimmers beat micro-swimmers

Surface interactions provide a class of mechanisms which can be employed for propulsion of micro- and nanometer sized particles. We investigate the related efficiency of externally and self-propelled swimmers. A general scaling relation is derived showing that only swimmers whose size is comparable to, or smaller than, the interaction range can have appreciable efficiency. An upper bound for efficiency at maximum power is 1/2. Numerical calculations for the case of diffusiophoresis are found to be in good agreement with analytical expressions for the efficiency

Development of an RF IV waveform based stress test procedure for use on GaN HFETs

This paper reports on the development of an RF IV waveform based stress test procedure. DC and low-voltage RF characterisation was carried out before and after high power RF stress. RF waveform measurements showed that the exact change in the RF load line induced during RF degradation cannot be directly inferred from the DC or low power RF measurement. The RF degradation takes the form of a knee-walkout, a small pinch-off shift consistent with charge trapping and defect generation, and in addition gate leakage occurs once the RF voltage exceeds a critical voltage

Productive resources in students’ ideas about energy: An alternative analysis of Watts’ original interview transcripts

For over 30 years, researchers have investigated students’ ideas about energy with the intent of reforming instructional practice. In this pursuit, Watts contributed an influential study with his 1983 paper “Some alternative views of energy” [Phys. Educ. 18, 213 (1983)]. Watts’ “alternative frameworks” continue to be used for categorizing students’ non-normative ideas about energy. Using a resources framework, we propose an alternate analysis of student responses from Watts’ interviews. In our analysis, we show how students’ activated resources about energy are disciplinarily productive. We suggest that fostering seeds of scientific understandings in students’ ideas about energy may play an important role in their development of scientific literacy

Students Talk about Energy in Project- Based Inquiry Science

We examine the types of emergent language eighth grade students in rural Maine middle schools use when they discuss energy in their first experiences with Project-Based Inquiry Science: Energy, a research-based curriculum that uses a specific language for talking about energy. By comparative analysis of the language used by the curriculum materials to students’ language, we find that students’ talk is at times more aligned with a Stores and Transfer model of energy than the Forms model supported by the curriculum

Acetylene chemistry in remote plasmas : implications for the a-C:H growth mechanism

The primary aim of this thesis is to contribute to the knowledge of the plasma assisted growth mechanism of carbon based thin films. This is achieved by means of studying the plasma chemistry in an Ar/C2H2 Expanding Thermal Plasma (ETP) used for deposition of hydrogenated amorphous carbon (a-C:H) and relating the measured hydrocarbon radical density quantitatively to the observed growth rate and film properties. The plasma composition has been studied by means of two ultra-sensitive techniques, which have been specifically designed and constructed for this purpose: Cavity Ringdown absorption Spectroscopy (CRDS) and Threshold Ionization Mass Spectrometry (TIMS). The ETP technique has been selected for its unusual high deposition rate (up to 70 nm/s), low electron temperature allowing to neglect all electron impact induced dissociation processes, the absence of energetic ion bombardment, the near ideal plug-down geometry suitable for straightforward quasi one-dimensional modeling of the plasma chemistry and the remote plasma character enabling an easy independent parameter study. CRDS has been applied to measure with high sensitivity C, CH and C2 radicals and to study the broadband absorption feature observed in the ETP. However, the range of the species, which can be measured by means of CRDS, is limited by existence of optical transitions in the spectral region accessible by the laser system used. A triple stage TIMS diagnostics was designed and constructed to complete the understanding of the plasma chemistry. In order to make quantitative measurements a novel background signal correction and an absolute density calibration procedure was developed and applied. In this study previous results were corroborated, i.e. the primary C2H2 decomposition is argon ion induced in subsequent charge transfer (CT) and dissociative recombination (DR) steps, and new insights in the plasma chemistry have evolved. The measurements presented in this thesis lead further to the hypothesis that C and C2 radicals are formed in similar amount as C2H in the primary C2H2 decomposition, a consequence of additional internal energy available in the CT and DR reactions. It was further confirmed that the plasma composition and film properties are determined by the ratio of the C2H2 flow and the argon ion and electron fluence emanating from the plasma source. Two limiting cases related to the ratio between the injected C2H2 flow and argon and electron fluence are observed. On the one hand, if the C2H2 flow into the reactor is smaller then emanating argon ion and electron fluence, the C2H2 is fully depleted and decomposed into C, C2, C2H and CH radicals. These radicals are then responsible for the growth of soft polymer-like a-C:H films, as confirmed by film property measurements. On the other hand, if the C2H2 flow is larger than the argon ion and electron fluence, C2H2 is abundantly present in the gas phase and the reactions of the primarily formed radicals (C, CH, C2 and C2H) with C2H2 determine the plasma composition close to the substrate. Two plasma chemistry branches have been identified in the latter case. In the first branch reactions of C2 and C2H radicals with C2H2 lead to the formation of stable diacetylene (C4H2) and further reactive C4 and C4H radicals. Stable hydrocarbon molecules with an even number of carbon atoms (C2nH2), which are commonly measured in C2H2 plasmas, are formed in this branch. The observed high gas phase reactivity of C2H, C4 and C4H hydrocarbon radicals excludes them from being the dominant growth precursors in an Ar/C2H2 ETP, falsifying the previous film growth hypothesis based on the C2H radical. The other branch involves reactions of C and CH radicals with C2H2 to form C3 and C3H radicals as products. These radicals are found to be abundantly present close to the substrate, since they are resonantly stabilized and hence unreactive in the gas phase with C2H2 and other stable hydrocarbons. The C5 and C5H radicals, formed most probably in reactions of C and CH with C4H2, show a similar behavior. The proposed plasma chemistry scheme has been successfully tested by means of a quasi one-dimensional plasma chemistry simulation model. Quantitatively the C3 radical density close to the substrate is found to be the highest among all radicals measured. Since the C3 density behavior as function of the acetylene flow mimics the measured film growth rate, the C3 radical is proposed to contribute significantly to the growth of hard a-C:H film. The film analysis results imply that hydrogen has to be incorporated into the growing film in order to explain the hydrogen content of about 30% for the best quality films. However, further research is required to understand whether hydrogen atoms or additional hydrogen containing species are incorporated during the film growth process

Bosonic Gaussian states from conformal field theory

We study nonchiral wave functions for systems with continuous spins obtained from the conformal field theory (CFT) of a free, massless boson. In contrast to the case of discrete spins, these can be treated as bosonic Gaussian states, which allows us to efficiently compute correlations and entanglement properties both in one (1D) and in two spatial dimensions (2D). In 1D, the computed entanglement entropy and spectra are in agreement with the underlying CFT. Furthermore, we construct a 1D parent Hamiltonian with a low-energy spectrum corresponding to that of a free, massless boson. In 2D, we find edge excitations in the entanglement spectrum, although the states do not have intrinsic topological order, as revealed by a determination of the topological entanglement entropy.Comment: 18 pages, 8 figures, v2: accepted versio

Argon metastable dynamics in a filamentary jet micro-discharge at atmospheric pressure

Space and time resolved concentrations of Ar ($^{3}P_2$) metastable atoms at the exit of an atmospheric pressure radio-frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. The discharge features a coaxial geometry with a hollow capillary as an inner electrode and a ceramic tube with metal ring as outer electrode. Absorption profiles of metastable atoms as well as optical emission measurements reveal the dynamics and the filamentary structure of the discharge. The average spatial distribution of Ar metastables is characterized with and without a target in front of the jet, showing that the target potential and therewith the electric field distribution substantially changes the filaments' expansion. Together with the detailed analysis of the ignition phase and the discharge's behavior under pulsed operation, the results give an insight into the excitation and de-excitation mechanisms

The Interaction of Genetic Background and Mutational Effects in Regulation of Mouse Craniofacial Shape.

Inbred genetic background significantly influences the expression of phenotypes associated with known genetic perturbations and can underlie variation in disease severity between individuals with the same mutation. However, the effect of epistatic interactions on the development of complex traits, such as craniofacial morphology, is poorly understood. Here, we investigated the effect of three inbred backgrounds (129X1/SvJ, C57BL/6J, and FVB/NJ) on the expression of craniofacial dysmorphology in mice (Mus musculus) with loss of function in three members of the Sprouty family of growth factor negative regulators (Spry1, Spry2, or Spry4) in order to explore the impact of epistatic interactions on skull morphology. We found that the interaction of inbred background and the Sprouty genotype explains as much craniofacial shape variation as the Sprouty genotype alone. The most severely affected genotypes display a relatively short and wide skull, a rounded cranial vault, and a more highly angled inferior profile. Our results suggest that the FVB background is more resilient to Sprouty loss of function than either C57 or 129, and that Spry4 loss is generally less severe than loss of Spry1 or Spry2 While the specific modifier genes responsible for these significant background effects remain unknown, our results highlight the value of intercrossing mice of multiple inbred backgrounds to identify the genes and developmental interactions that modulate the severity of craniofacial dysmorphology. Our quantitative results represent an important first step toward elucidating genetic interactions underlying variation in robustness to known genetic perturbations in mice