12,649 research outputs found
Disproportionate Frequency Representation in the Inferior Colliculus of Doppler-Compensating Greater Horseshoe Bats. Evidence for an Acoustic Fovea
1. The inferior colliculus of 8 Greater Horseshoe bats (Rhinolophus ferrumequinun) was systematically sampled with electrode penetrations covering the entire volume of the nucleus. The best frequencies and intensity thresholds for pure tones (Fig. 2) were determined for 591 neurons. The locations of the electrode penetrations within the inferior colliculus were histologically verified.
2. About 50% of all neurons encountered had best frequencies (BF) in the frequency range between 78 and 88 kHz (Table 1, Fig. 1A). Within this frequency range the BFs between 83.0 and 84.5 kHz were overrepresented with 16.3% of the total population of neurons (Fig. 1B). The frequencies of the constant frequency components of the echoes fall into this frequency range.
3. The representation of BFs expressed as number of neurons per octave shows a striking correspondence to the nonuniform innervation density in the afferent innervation of the basilar membrane (Bruns and Schmieszek, in press). The high innervation density of the basilar membrane in the frequency band between 83 and 84.5 kHz coincides with the maximum of the distribution of number of neurons per octave across frequency in the inferior colliculus (Fig. 1 C).
4. The disproportionate representation of frequencies in the auditory system of the greater horseshoe bat is described as an acoustical fovea functioning in analogy to the fovea in the visual system. The functional importance of the Doppler-shift compensation for such a foveal mechanism in the auditory system of horseshoe bats is related to that of tracking eye movements in the visual system
Coding of Small Sinusoidal Frequency and Amplitude Modulations in the Inferior Colliculus of 'CF-FM' Bat, Rhinolophus Ferrumequinum
Single neurons in the inferior colliculus of the Greater Horseshoe bat, Rhinolophus ferrumequinum, showed two broad categories of response patterns to sinusoidally frequency (SFM) or amplitude (SAM) modulated stimuli. Tonic responding cells (best excitatory frequency (BEF) between 10 and 90 kHz) showed a rough sinusoidal modulation of the discharge pattern to SFM. Transient responding neurons, generally showing on- or off-responses to pure tones, (BEF between 65 and 88 kHz), displayed highly synchronized discharge patterns to SFM-cycles (Fig. 1). Modulation rates between 20 and 100 Hz were most effective and some neurons encoded modulation rates up to 350 Hz (Figs. 2 and 3). The SFM responses were best synchronized to the modulation envelope for center frequencies in the upper portion of the tuning curve (Figs. 4 and 5). Sharply tuned neurons with BEF around 80 kHz had the lowest threshold for modulation depth (± 10 Hz or 0.025%) (Fig. 6). In general, SAMs evoked the same type of response patterns and were encoded down to modulation index of 3% (Fig. 7). The fine frequency and amplitude discriminations for periodical modulations by collicular neurons is discussed as related to the detection and discrimination performance of bats, when preying on flying insects in clustered surroundings
Line-shape analysis of charmonium resonances
We discuss weather the new enhancements found by BES, alias the ,
, , and are true resonances. We argue that the
nearby thresholds , ,
and , as well as
the and states have a strong influence over the
observed and line-shapes. We propose an
unitarized effective Lagrangian model to study the dynamical effect of the
interaction between each known state and its closest thresholds. In
addition, we present some of our recent motivating results, using the same
model, for the resonance, where the distortion from a Breit-Wigner
line-shape is shown to result not only from the kinematic interference, but
also from the influence of the one-loops. Moreover, two
poles were found, at about 3.78 GeV and at 3.74 GeV, the second one generated
dynamically, yet contributing to the distortion of the line-shape.Comment: Proceedings of the Conference "Hadron 17", held on 25-29 September,
2017, in Salamanca, Spai
Hunting for exotic doubly hidden-charm/bottom tetraquark states
We develop a moment QCD sum rule method augmented by fundamental inequalities
to study the existence of exotic doubly hidden-charm/bottom tetraquark states
made of four heavy quarks. Using the compact diquark-antidiquark configuration,
we calculate the mass spectra of these tetraquark states. There are 18
hidden-charm tetraquark currents with ,
, , , , , , and . We
use them to perform QCD sum rule analyses, and the obtained masses are all
higher than the spontaneous dissociation thresholds of two charmonium mesons,
which are thus their dominant decay modes. The masses of the corresponding
hidden-bottom tetraquarks are all below or very close to the
thresholds of the and , except
one current of . Hence, we suggest to search for the doubly
hidden-charm states in the and channels.Comment: 5 pages, 3 figures and 2 tables. published in PL
Constructing cities, deconstructing scaling laws
Cities can be characterised and modelled through different urban measures.
Consistency within these observables is crucial in order to advance towards a
science of cities. Bettencourt et al have proposed that many of these urban
measures can be predicted through universal scaling laws. We develop a
framework to consistently define cities, using commuting to work and population
density thresholds, and construct thousands of realisations of systems of
cities with different boundaries for England and Wales. These serve as a
laboratory for the scaling analysis of a large set of urban indicators. The
analysis shows that population size alone does not provide enough information
to describe or predict the state of a city as previously proposed, indicating
that the expected scaling laws are not corroborated. We found that most urban
indicators scale linearly with city size regardless of the definition of the
urban boundaries. However, when non-linear correlations are present, the
exponent fluctuates considerably.Comment: Accepted for publication, Journal of the Royal Society Interfac
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