Model-based detection of synthetic bat echolocation calls using an energy threshold detector for initialization

Detection of echolocation calls is fundamental to quantitative analysis of bat acoustic signals. Automated methods of detection reduce the subjectivity of hand labeling of calls and speed up the detection process in an accurate and repeatable manner. A model-based detector was initialized using a baseline energy threshold detector, removing the need for hand labels to train the model, and shown to be superior to the baseline detector using synthetic calls in two experiments: (1) an artificial environment and (2) a field playback setting. Synthetic calls using a piecewise exponential frequency modulation function from five hypothetical species were employed to control the signal-to-noise ratio (SNR) in each experiment and to provide an absolute ground truth to judge detector performance. The model-based detector outperformed the baseline detector by 2.5 dB SNR in the artificial environment and 1.5 dB SNR in the field playback setting. Atmospheric absorption was measured for the synthetic calls, and 1.5 dB increased the effective detection radius by between 1 and 7 m depending on species. The results demonstrate that hand labels are not necessary for training detection models and that model-based detectors significantly increase the range of detection for a recording system.     

A reverse Denjoy theorem II

For α satisfying 0 < α < π, suppose that C ₁ and C ₂ are rays from the origin, C ₁: z = re ^i(π−α) and C ₂: z = re ^i(π+α), r ≥ 0, and that D = {z: | arg z − π| < α}. Let u be a nonconstant subharmonic function in the plane and define B(r, u) = sup_|z|=r u(z) and A _D (r, u) = $ \inf _{z \in \bar D_r } $ \inf _{z \in \bar D_r } u(z), where D _r = {z: z ∈ D and |z| = r}. If u(z) = (1 + o(1))B(|z|, u) as z → ∞ on C ₁ ∪ C ₂ and A _D (r, u) = o(B(r, u)) as r → ∞, then the lower order of u is at least π/(2α).     

Aperiodic stochastic resonance in a hysteretic population of cardiac neurons

Aperiodic stochastic resonance (ASR) is studied for a densely interconnected population of excitatory and inhibitory neurons that exhibit hysteresis. Switching between states in the presence of noisy external forcing is represented as a "competition between averages" and this is further explained through a semianalytical model. In contrast to energy-based approaches where only the timing of a switch between states is represented, the competition between averages also identifies the input history responsible for a switch. This last point leads to some interesting conclusions regarding cause and effect in the presence of noisy forcing of a hysteretic system. For example, at subthreshold inputs, it is found that the input history causing a switch between states is primarily dependent upon the noise level even though the corresponding time to switch is sensitive to both the distance from the threshold and the noise level. Since the application considered here is to cardiac neuronal control, control performance is considered over the full input range. Noise tuning for adequate control performance is found to be unnecessary if the noise level is high enough. This is consistent with studies of ASR for sensory neurons. Another observation made here that may be of clinical significance is that at higher noise levels, constraints placed upon inputs to ensure adequate control performance are likely to depend upon the switching direction.     

Diagnostic ultrasound artifacts during imaging of two-body interfaces: part 1--wavelength resonance

A diagnostic ultrasound technique is to be developed for measuring surface contact areas at the tibio-femoral interface of a total knee replacement in an in vitro industrial engineering setting as a design tool. As a first step, a previous study mathematically characterized the ultrasound behaviour expected at a two-body circular-on-flat interface of known geometry. In the current investigation, a series of test objects was constructed and imaged to experimentally validate the theoretical contact models. Specifically, several unique metal-on-polymer test objects, whose interfaces were point, non-point, and circular contact areas, were ultrasonically imaged. The effects of interface geometry, ultrasound resonance wavelength, λ/2, and compressive load were studied.     

Two-hole strengths in K from the K(He, αK reaction

States in ³⁸K up to 7.13 MeV excitation have been studied using the 21 MeV ³He⁺⁺ beam of a tandem Van de Graaff and the ³⁹K(³He, α) reaction. Charged particles were analysed by a split-pole magnetic spectrograph equipped with a telescope arrangement of proportional counters for position and energy-loss measurement.     

Investigations into the interactions between DNA and conformationally constrained pyridylamineplatinum(II) analogues of AMD473

The syntheses of [PtCl(2)(amp)] (amp = 2-pyridylmethylamine) and enantiomerically pure [PtCl(2)(R-pea)] and [PtCl(2)(S-pea)] (pea = 1-(2-pyridyl)ethylamine) and the crystal structure of [PtCl(2)(R-pea)] are reported. The reactions of [PtCl(2)(amp)] and of the enantiomers of [PtCl(2)(pea)] with d(GpG) and with a 52-base-pair oligonucleotide were investigated. Each of the reactions with d(GpG) resulted in the formation of three platinated bifunctional d(GpG) species in a ratio of 1:2:1. These species were shown to be a pair of isomers, one of which exists as a pair of slowly interconverting rotamers that can be separated by HPLC but reequilibrate after 5 days at 37 degrees C. The pyridyl moieties of the pyridylalkylamine ligands are constrained to lie in the coordination plane, and as a consequence, the rotation about the Pt-N7 bond of the adjacent guanine is highly restricted. 2D NMR investigations were carried out on the isomer of [Ptd(GpG)(amp)] that did not form separable rotamers and identified it as the isomer having the pyridine adjacent to the 5'-guanine of the d(GpG). The reaction of each of the three [PtCl(2)(py-R)] complexes (py-R = amp or pea) with a 52-base-pair oligonucleotide resulted in the formation of the same three bifunctional d(GpG) adducts in approximately the same ratios as the reactions with d(GpG), indicating that negligible stereoselectivity results from interactions between the complexes and duplex DNA.     

The synthesis and structure of 5-hydroxy-2-methyl-2-(2-pyridinyl)hexahydro-1,3-pyrimidine

The synthesis and the x-ray structure of 5-hydroxy-2-methyl-(2-pyridinyl)hexahydro-1,3-pyrimidine are reported. The compound was prepared by reaction of 2-acetylpyridine and 1,3-diamino-2-hydroxypropane in a 2:1 molar ratio. The colourless crystals are monoclinic, space group P2₁/c with cell parameters, a = 10.385(5), b = 11.171(5), c = 17.415(6)Å, β = 93.05(37)° for Z = 8. The asymmetric unit of the structure is composed of two independent molecules of the compound which are in the chair form and adopt the same conformation with equatorial -OH and -CH₃ groups and axial pyridine substituents. The packing of the molecule seems to be controlled by two independent hydrogen-bonding sequences.