Sensing clouds: A distributed cooperative target tracking with tiny binary noisy sensors

This paper suggests a novel algorithm for mobile object tracking using wireless sensor networks (WSNs). The paper assumes a future model of WSNs, where a large number of low to medium range inexpensive and noisy sensors are distributed randomly over an area. The distributed algorithm is based on short range communication between neighboring sensors, and is designed to work with very basic low cost binary sensors, that can report only a sensing, not sensing value.Neighboring sensors that sense the object form a cloud around the object which is dynamically updated as the object moves. To save energy on reporting a subset of the cloud, the cloud core, is elected. A trade-off between the accuracy and the core size (namely transmission power) is presented, as well as an extensive simulation study. Our algorithm works well with false negative sensing and up to 10% false positive sensing.     

Permutation statistics on the alternating group

Let A_nS_n denote the alternating and the symmetric groups on 1,…,n. MacMahon's theorem [P.A. MacMahon, Combinatory Analysis I–II, Cambridge Univ. Press, 1916], about the equi-distribution of the length and the major indices in S_n, has received far reaching refinements and generalizations, by Foata [Proc. Amer. Math. Soc. 19 (1968) 236], Carlitz [Trans. Amer. Math. Soc. 76 (1954) 332; Amer. Math. Monthly 82 (1975) 51], Foata-Schützenberger [Math. Nachr. 83 (1978) 143], Garsia–Gessel [Adv. Math. 31 (1979) 288] and followers. Our main goal is to find analogous statistics and identities for the alternating group A_n. A new statistics for S_n, the delent number, is introduced. This new statistics is involved with new S_n identities, refining some of the results in [D. Foata, M.P. Schützenberger, Math. Nachr. 83 (1978) 143; A.M. Garsia, I. Gessel, Adv. Math. 31 (1979) 288]. By a certain covering map , such S_n identities are ‘lifted’ to A_n+1, yielding the corresponding A_n+1 equi-distribution identities.     

Design and optimization for variable rate selective excitation using an analytic RF scaling function

At higher B(0) fields, specific absorption rate (SAR) deposition increases. Due to maximum SAR limitation, slice coverage decreases and/or scan time increases. Conventional selective RF pulses are played out in conjunction with a time independent field gradient. Variable rate selective excitation (VERSE) is a technique that modifies the original RF and gradient waveforms such that slice profile is unchanged. The drawback is that the slice profile for off-resonance spins is distorted. A new VERSE algorithm based on modeling the scaled waveforms as a Fermi function is introduced. It ensures that system related constraints of maximum gradient amplitude and slew rate are not exceeded. The algorithm can be used to preserve the original RF pulse duration while minimizing SAR and peak b1 or to minimize the RF pulse duration. The design is general and can be applied to any symmetrical or asymmetrical RF waveform. The algorithm is demonstrated by using it to (a) minimize the SAR of a linear phase RF pulse, (b) minimize SAR of a hyperbolic secant RF pulse, and (c) minimize the duration of a linear phase RF pulse. Images with a T1-FLAIR (T1 FLuid Attenuated Inversion Recovery) sequence using a conventional and VERSE adiabatic inversion RF pulse are presented. Comparison of images and scan parameters for different anatomies and coils shows increased scan coverage and decreased SAR with the VERSE inversion RF pulse, while image quality is preserved.     

REACTIVITY OF SINGLET OXYGEN TOWARD AMINO ACIDS AND PEPTIDES

Quenching of singlet oxygen (¹O₂) in D₂O-ethanol by the amino acids tryptophan, tyrosine, histidine, methionine, cysteine and their derivatives was measured by exciting the sensitizers rose bengal or meso-tetra (N-methyl-4-pyridyl)porphyrin tetratosylate in the presence of oxygen and the above quenchers in solution. In our polar solvent, containing 75% D₂O on a molar basis it was found that (1) substitution of the aromatic ring in indole, phenol and imidazole by the electron-donating methyl group increases the total (i.e. nonreactive and reactive) quenching rate constant by a factor of five to eight. Free or blocked amino and carboxyl groups removed by two methylene groups from the ring counteract the above increase in the rate constant. The reactive quenching of singlet oxygen, which leads to oxidative destruction of the aromatic ring, correlates with the above substitution effects. It has been proposed that the quenching process takes place by formation of an exciplex between ¹O₂ and the quencher. Thus our results indicate that the better an electron donor the amino acid residue is the more pronounced is the charge transfer contribution in the exciplex formed with ¹O₂ and the more likely it is to lead to charge separation and hence to a chemical reaction. (2) Oligopeptides in solution or peptide bonds linked to the amino acid residue have only a minor effect on singlet oxygen. It can therefore be expected that the polypeptide chains per se in the protein network will not interact significantly with the single oxygen molecules present. The quenching of the latter should, to a first approximation, depend only on the presence of the above reactive amino acid residues and to their accessibility to ¹O₂ as well as on the effective dielectric constant within the protein structure.     

Transverse relaxation in the rotating frame induced by chemical exchange

In the presence of radiofrequency irradiation, relaxation of magnetization aligned with the effective magnetic field is characterized by the time constant T1rho. On the other hand, the time constant T2rho characterizes the relaxation of magnetization that is perpendicular to the effective field. Here, it is shown that T2rho can be measured directly with Carr-Purcell sequences composed of a train of adiabatic full-passage (AFP) pulses. During adiabatic rotation, T2rho characterizes the relaxation of the magnetization, which under adiabatic conditions remains approximately perpendicular to the time-dependent effective field. Theory is derived to describe the influence of chemical exchange on T2rho relaxation in the fast-exchange regime, with time constant defined as T2rho,ex. The derived theory predicts the rate constant R2rho,ex (= 1/T2rho,ex) to be dependent on the choice of amplitude- and frequency-modulation functions used in the AFP pulses. Measurements of R2rho,ex of the water/ethanol exchanging system confirm the predicted dependence on modulation functions. The described theoretical framework and adiabatic methods represent new tools to probe exchanging systems.     

The trace of spatial brownian motion is capacity-equivalent to the unit square

Summary. We show that with probability 1, the trace B[0, 1] of Brownian motion in space, has positive capacity with respect to exactly the same kernels as the unit square. More precisely, the energy of occupation measure on B[0, 1] in the kernel f(∣x−y∣), is bounded above and below by constant multiples of the energy of Lebesgue measure on the unit square. (The constants are random, but do not depend on the kernel.) As an application, we give almost-sure asymptotics for the probability that an α-stable process approaches within ɛ of B[0, 1], conditional on B[0, 1]. The upper bound on energy is based on a strong law for the approximate self-intersections of the Brownian path. We also prove analogous capacity estimates for planar Brownian motion and for the zero-set of one-dimensional Brownian motion. Received: 8 February 1995 / In revised form: 27 July 1995     

Electrodeposited quantum dots IV. Epitaxial short-range order in amorphous semiconductor nanostructures

The structure of diffraction-amorphous CdSe (a-CdSe) quantum dots (QDs) electrodeposited on evaporated Pd substrate was studied by high resolution transmission electron microscopy (HRTEM), and compared with epitaxial (crystalline) QDs obtained by the same procedure on Au, as well as with a simulated image of random a-CdSe. Digital analysis of HRTEM images established the existence of repeating ordered motifs in a-CdSe QDs on Pd substrates, in the form of epitaxial sub-nanometre to nanometre size clusters. The QDs are shown to be intermediate between crystalline and random amorphous material. Digital Fourier analysis indicated epitaxial relationship with the 111inPd substrate, rotated 30° relative to the orientational relationship on 111_Au.