Ultrasound sensitivity in the cricket, Eunemobius carolinus (Gryllidae, Nemobiinae)

Extracellular recordings from the cervical connectives in both long- and short-winged E. carolinus reveal auditory units that are sensitive to frequencies > 15 kHz with best sensitivity at 35 kHz (79 dB SPL threshold). Stimuli in this frequency range also elicit a startle response in long-winged individuals flying on a tether. For single-pulse stimuli, startle and neck connective thresholds decrease with increasing ultrasound duration, consistent with the operation of an exponential integrator with a approximately 32.5-ms time constant. There is evidence for adaptation to long duration pulses (> 20 ms) in the neck connectives, however, as it is more difficult to elicit responses to the later stimuli of a series. For paired-pulse stimuli consisting of 1-ms pulses of 40 kHz, temporal integration was demonstrated for pulse separations < 5 ms. For longer pulse separations, startle thresholds were elevated by 3 dB and appear to be optimally combined. Startle thresholds to 5 ms frequency modulated (FM) sweeps (60-30 kHz) and pure tone pulses (40 kHz) did not differ. The characteristics and sensitivity of this ultrasound-induced startle response did not differ between males and females. As in some other tympanate insects, ultrasound sensitivity in E. carolinus presumably functions in the context of predation from echolocating bats.     

Two-tone suppression in auditory nerve of the cat: rate-intensity and temporal analyses

Responses to two-tone stimuli were recorded from auditory-nerve fibers in anesthetized cats. One tone, the suppressor, was set at a frequency above characteristic frequency and was fixed in intensity. A second tone was set at an excitatory frequency and was varied in intensity. The suppressor tone, when set at a sufficient level, always reduced the response to the excitatory tone by an amount equivalent to a fixed number of decibels, regardless of the excitatory tone's intensity. Estimates of suppression magnitude were derived from shifts in rate-intensity function obtained when the suppressor tone was present relative to the functions obtained for the excitatory tone alone. When suppressor-tone intensity was increased, suppression magnitude likewise increased. When the two tones were increasingly separated in frequency, either by varying the excitor or by varying the suppressor, suppression magnitude decreased monotonically. Suppression behaved in the same manner regardless of whether suppresor tone was excitatory or nonexcitatory. When frequency separation was small enough and when both tones were above the neuron's characteristic frequency, responses synchronized to low-order combination tones could be elicited. These responses usually possessed different rate-intensity characteristics and resulted in estimates of suppression magnitude which were spuriously low. When frequency separation is normalized with regard to position of traveling wave maxima within the cochlear duct, the magnitude of two-tone suppression for a given suppressor-tone intensity is seen to be frequency independent.     

Acoustical analysis of the auditory system of the cricket Teleogryllus commodus (Walker)

The basic auditory physiology of crickets, and particularly of Teleogryllus commodus (Walker) is examined and its behavior simulated by electrical analog networks, beginning from the simplest possible model and progressing by stages to the full system found in the real insect. It is found that the attenuation of sound in the auditory trachea plays a crucial role in the mechanism for directional hearing in even the simplest model and that the tracheal diameter is in fact appropriate to produce the desired attenuation. In a more complex model in which it is recognized that the auditory system probably responds to pressure changes in the tracheal sacs underlying the tympana rather than simply to tympanic motion, it is found that the phase shift produced by the combined effects of the central septum and the adjoining cavities leading to the spiracles is also important to hearing directionality. The final model which includes both tympana and spiracles is able to simulate both the hearing directionality and, in part, the frequency selectivity of the system. It appears, however, that a large measure of the observed frequency selectivity is due to some form of selectivity in the neural transducers themselves rather than in the simple acoustic components of the system.     

Quark-matter diagnostics: Dileptons,photons and (JΨ) suppression

The appropriate kinematic window for dileptons and photons, and possible signals of quarkgluon plasma are discussed. A suppression ofJ/Ψ, entirely due to hadronic matteris also discussed.     

Total suppression of superconductivity by high magnetic fields in YBa(2)Cu(3)O(6.6)

We have studied the variation of transverse magnetoresistance of underdoped YBCO(6.6) crystals, either pure or with reduced T(c) down to 3.5 K by electron irradiation, in fields up to 60 T. We find evidence that the superconducting fluctuation contribution to the conductivity is suppressed only above a threshold field H(c)'(T), which is found to vanish at T(c)' > T(c). In the pure YBCO(6.6) sample, H(c)' is already 50 T at T(c). We find that increasing disorder weakly depresses H(c)'(0), T(c)', and T(nu), the onset of the Nernst signal. Thus, these energy scales appear more characteristic of the 2D local pairing than the pseudogap temperature which is not modified by disorder.     

Convection-compensating PGSE experiment incorporating excitation-sculpting water suppression (CONVEX)

We present a new diffusion experiment which provides simultaneous suppression of an on-resonance solvent peak and compensation for convection. The experiment, which we name CONVEX, exploits similarities between two functionally different pulse sequences to enable the same sequence to be used simultaneously for two different purposes. The CONVEX pulse sequence combines a double-echo PGSE with double excitation-sculpting water suppression, using unequal gradient pulse-pair amplitudes (g1 and g2) and unequal diffusion intervals (Delta1 and Delta2). Convection compensation is achieved by setting g1:g2 = Delta2:Delta1. The new experiment provides the spectral quality, flat baseline, and water-suppression power characteristic of excitation-sculpting experiments, combined with excellent compensation for convection. The resulting Stejskal-Tanner plots are linear over a greater range of signal attenuation than in the absence of water suppression. Possible applications include protein NMR; NMR of cellular or colloidal systems; and the monitoring of technological processes.     

Fire suppression using trifluoroiodomethane (CF3I)-carbon dioxide (CO2) mixtures

With the regulatory prohibition for using Halon 1301 (CF₃Br) in fire suppression systems onboard newly certified aircraft, significant research efforts have been undertaken to develop suitable halon replacements with comparable suppression performance that are also eco-friendly with low Ozone Depletion Potential (ODP) and Global Warming Potential (GWP). This paper determined the fire suppression effectiveness for mixtures of trifluoroiodomethane (CF₃I) with carbon dioxide (CO₂) under development as a drop-in halon replacement for onboard aircraft fire suppression systems. Through both experimental measurements and flame simulations using detailed chemical kinetics, we demonstrated that the extinguishment performance of CF₃I-CO₂ blends can be superior to that of the individual components alone. The extinction concentrations were determined for different CF₃I-to-CO₂ ratios introduced into ambient air using a heptane cup burner. The extinction concentrations for pure CF₃I in air (3.36 ± 0.13% vol.) and CO₂ in air (20.74 ± 0.64% vol.) are in close agreement with previously reported values, and first-time extinction concentration data for CF₃I-CO₂ blends are reported. To elucidate important reaction pathways, detailed chemical mechanisms have been compiled for modeling methane-, propane- and heptane-air flame inhibition at ambient conditions. These mechanisms were constructed from published sub-mechanisms for C₇ and C₁-C₃ hydrocarbons and hydrofluorocarbons with additional oxidation chemistry developed for trifluoroiodomethane. The latter sub-mechanism contains 14 species and 91 reactions. Using the CANTERA software package, critical concentration values of CF₃I-CO₂ mixtures in air for extinguishing methane, propane, and n-heptane counterflow flames were determined and compared against experimental non-premixed flame extinction data.     

Selective mode suppression in microstrip differential lines by means of electric-LC (ELC) and magnetic-LC (MLC) resonators

In this paper, it is demonstrated that the so-called electric-LC (ELC) resonators, and their dual counterparts, the magnetic-LC (MLC) resonators, are useful for the selective suppression of either the differential or the common mode in microstrip differential lines. The key point to mode suppression is the alignment of the resonator with the electric (differential mode) or magnetic (common mode) wall of the line. It is shown that by simply rotating the resonators 90^° we can selectively choose the suppressed mode in the vicinity of the resonator’s fundamental resonance frequency. The theory is validated through full-wave electromagnetic simulation, the lumped element equivalent circuit models of the proposed structures and experimental data.     

Three-dimensional protein NMR TROSY-type (15)N-resolved (1)H(N)-(1)H(N) NOESY spectra with diagonal peak suppression

An earlier two-dimensional NOESY experiment with diagonal peak suppression in the (1)H(N)-(1)H(N) region is extended to three dimensions by including (15)N evolution while maintaining the TROSY approach throughout. The technique suppresses all anti-TROSY resonances by appropriate pulse sequence elements and for large molecules at high fields possible semi- and anti-TROSY artifacts are further suppressed by virtue of much shorter transverse relaxation times for these components. The new technique is demonstrated using an (15)N-labeled protein sample, RAP 17-97 (N-terminal domain of alpha2-macroglobulin Receptor Associated Protein), in H(2)O at 500 MHz.     

Morin transition suppression in Polycrystalline 57Hematite (α-Fe2O3) exposed to 56Fe(II)

We used the isotope selectivity of ⁵⁷Fe Mössbauer spectroscopy to investigate changes in the magnetic properties of polycrystalline hematite exposed to ferrous iron (Fe(II)). We found that sorption of ⁵⁶Fe(II), followed by interfacial electron exchange, alters the bulk magnetic properties of ⁵⁷hematite. After reaction with ⁵⁶Fe(II), we observed partial suppression of the Morin transition of ⁵⁷hematite to below 13 K. This is significantly lower than the Morin temperature (T _M) of ～230 K measured for isotopically enriched polycrystalline ⁵⁷hematite, as well as the T _M of 264?±?2 K reported for normal polycrystalline hematite.     

Shubnikov-de Haas oscillations and the magnetic-field-induced suppression of the charge ordered state in Na(0.5)CoO2

We have performed electrical transport measurements at low temperatures and high magnetic fields in Na(0.5)CoO2 single crystals. Shubnikov-de Haas oscillations corresponding to only 1% of the area of the orthorhombic Brillouin zone were clearly observed, indicating that most of the original Fermi surface vanishes at the charge-ordering (CO) transition. In-plane magnetic fields were found to suppress strongly the CO state. For fields rotated within the conducting planes, we observe angular magnetoresistance oscillations whose periodicity changes from twofold to sixfold at the transition.     

The motion artifact suppression technique (MAST) in magnetic resonance imaging: clinical results

The Motion Artifact Suppression Technique (MAST) is a method which uses a series of gradient echos that are computed to cancel velocity, acceleration and pulsatility components of involuntary motion in MR imaging. A total of 916 patient studies were performed over a nine month period using MAST sequences with a TE 40, 60, 80, 100, 120, and 26/112. There was considerable improvement in long TR, long TE images. Cerebrospinal fluid flow artifacts were reduced. Body and spine images had reduced flow and respiratory artifacts. Spin rephasing in blood vessels caused increase intraluminal signal. This might be useful for cardiovascular imaging.