A medium access protocol exploiting multiuser-detection in CDMA ad-hoc networks

A new medium access protocol which exploits the physical layer capability of multiuser detection is proposed to help in improving the throughput/delay performance of ad-hoc networks. When more than one node has packets buffered for a common node in the neighborhood, all such nodes can simultaneously transmit their packets to the common receiver after reserving their surrounding channel. This is achieved in our protocol by extending the (sender-initiated) CSMA/CA collision avoidance framework by the receiver-initiated medium access technique and incorporating the transmission power control. We analyze the improvement in the throughput that can be achieved over the basic sender-initiated collision avoidance protocol in the network. Since the throughput improvement via multi-packet reception is influenced by the network layer activity as well, the performance of our protocol rolls back to that of the basic sender-initiated protocol in case of no coordination from the network layer. For the evaluation of performance of our protocol we simulate ad-hoc networks for different network topologies and traffic configurations. We observe the scheme to be capable in significantly improving the throughput/delay performance of the network.     

Kinetics of formation of barium tungstate in equimolar powder mixture of BaCO<Subscript>3</Subscript> and WO<Subscript>3</Subscript>

The formation of Barium monotungstate (BaWO₄) particles in equimolar powder mixtures of BaCO₃ and WO₃ was examined under isothermal and non-isothermal conditions upon heating in air at 25–1200 °C, using thermogravimetry. Concurrence of the observed mass loss (due to the release of CO₂) to the occurrence of the formation reaction was evidenced. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The x–t and x–T data thus obtained were processed using well established mathematical apparatus and methods, in order to characterize nature of reaction rate-determining step, and derive isothermal and non-isothermal kinetic parameters. Moreover, the reaction mixture quenched at various temperatures (600–1,000 °C) in the reaction course was analyzed by various spectroscopic and microscopic techniques, for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional diffusion of WO₃ species across the product layer (BaWO₄), which was implied to form on the barium carbonate particles. The isothermally determined activation energy (118–125 kJ/mol) was found to be more credible than that (245 kJ/mol) determined non-isothermally.     

Sensitivity enhancement of CE and CE-MS for the analysis of peptides by a dynamic pH junction

An analytical method of CE-MS and CE with an online preconcentration technique induced by a dynamic pH junction, addition of organic solvent and large volume injection was developed for sensitive determination of peptides in biological samples. Leucine enkephalin, methionine enkephalin, dynorphin A, β-endorphin and angiotensin II were used as model peptides. The optimal online preconcentration conditions were obtained at a sample matrix consisting of 100?mM borate buffer (pH 10.0) with 50% v/v acetonitrile and a BGE containing 1?M formic acid at pH 2.0, along with a 25-cm injection length. Under the optimized conditions, a 4.0×10(3)-1.1×10(4)-fold increase in peak intensity was achieved without degrading the peak shape. This online preconcentration method was applied to analyze the intracellular angiotensin II within the peptides extracted from HL1 cells and approximately increase of 1×10(4)-fold sensitivity was achieved compared to normal condition. Thus, the developed method could be applied to the analysis of various peptides for peptidomics study in biological samples.     

Two-step on-particle ionization/enrichment via a washing- and separation-free approach: multifunctional TiO2 nanoparticles as desalting, accelerating, and affinity probes for microwave-assisted tryptic digestion of phosphoproteins in ESI-MS and MALDI-MS: comparison with microscale TiO2

We introduce a simplified sample preparation method using bare TiO₂ nanoparticles (NPs) to serve as multifunctional nanoprobes (desalting, accelerating, and affinity probes) for effective enrichment of phosphopeptides from microwave-assisted tryptic digestion of phosphoproteins (α-casein, β-casein and milk) in Electrospray Ionization Mass Spectrometry (ESI-MS) and Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS). The results demonstrate that TiO₂ NPs can effectively enrich and accelerate the digestion reactions of phosphoproteins in aqueous solutions and also from complex real samples. After the microwave experiments, we directly injected the resulting solutions into the ESI-MS and MALDI-MS systems for analysis, and excellent sensitivity was achieved without the need for any washing procedure or separation process. The reasons are attributed to the high binding affinity and selectivity of TiO₂ NPs toward phosphopeptides. Thus, phosphopeptides can be adsorbed onto the TiO₂ NP surface. The digested or partially digested phosphoproteins can be concentrated onto the TiO₂ NP surface. This results in the effective or complete digestion of phosphoproteins in a short period of time (45 s). In addition, high sensitivity and sequence coverage of phosphopeptide can be obtained using TiO₂ NPs as microwave absorbers and affinity probes in MALDI-MS and ESI-MS. This is due to the photocatalytic nature of the TiO₂ NPs because the absorption of microwave radiation that can accelerate the activation of trypsin for efficient digestion of phosphoproteins and enhances the ionization of phosphopeptides. The lowest concentrations detected for ESI-MS and MALDI-MS were 0.1 μM and 10 fmol, respectively, for α-casein. Comparing the two-step approach of TiO₂ NPs with microscale TiO₂ particles, the microscale TiO₂ particles shows no effect on the microwave-assisted tryptic digestion of phosphoproteins. The current approach offers multiple advantages, such as great simplicity, high sensitivity and selectivity, straightforward and separation/washing-free technique for phosphorpeptide enrichment analysis.     

Structural properties of trans‐cyclohexane‐1,2‐diamine complexes of copper(II) and zinc(II) acesulfamates

The title compounds, trans‐bis(trans‐cyclohexane‐1,2‐diamine)bis(6‐methyl‐2,2,4‐trioxo‐3,4‐dihydro‐1,2,3‐oxathiazin‐3‐ido)copper(II), [Cu(C₄H₄NO₄S)₂(C₆H₁₄N₂)₂], (I), and trans‐diaquabis(cyclohexane‐1,2‐diamine)zinc(II) 6‐methyl‐2,2,4‐trioxo‐3,4‐dihydro‐1,2,3‐oxathiazin‐3‐ide dihydrate, [Zn(C₆H₁₄N₂)₂(H₂O)₂](C₄H₄NO₄S)₂·2H₂O, (II), are two‐dimensional hydrogen‐bonded supramolecular complexes. In (I), the Cu^II ion resides on a centre of symmetry in a neutral complex, in a tetragonally distorted octahedral coordination environment comprising four amine N atoms from cyclohexane‐1,2‐diamine ligands and two N atoms of two acesulfamate ligands. Intermolecular N—H...O and C—H...O hydrogen bonds produce R₂²(12) motif rings which lead to two‐dimensional polymeric networks. In contrast, the Zn^II ion in (II) resides on a centre of symmetry in a complex dication with a less distorted octahedral coordination environment comprising four amine N atoms from cyclohexane‐1,2‐diamine ligands and two O atoms from aqua ligands. In (II), an extensive two‐dimensional network of N—H...O, O—H...O and C—H...O hydrogen bonds includes R₂¹(6) and R₄⁴(16) motif rings.     

Hierarchical quantization indexing for wavelet and wavelet packet image coding

In this paper, we introduce the quantization index hierarchy, which is used for efficient coding of quantized wavelet and wavelet packet coefficients. A hierarchical classification map is defined in each wavelet subband, which describes the quantized data through a series of index classes. Going from bottom to the top of the tree, neighboring coefficients are combined to form classes that represent some statistics of the quantization indices of these coefficients. Higher levels of the tree are constructed iteratively by repeating this class assignment to partition the coefficients into larger subsets. The class assignments are optimized using a rate-distortion cost analysis. The optimized tree is coded hierarchically from top to bottom by coding the class membership information at each level of the tree. Context-adaptive arithmetic coding is used to improve coding efficiency. The developed algorithm produces PSNR results that are better than the state-of-art wavelet-based and wavelet packet-based coders in literature.     

保护家电和专业电子系统组件的利器—协同电路保护方案

在各种家电和各种专业设备中的电机、控制器和诸多的电子部件,均可得益于所用的协同电路保护。如今的高分子正温度系数（PPTC）过电流保护部件,能够提供极低的电阻．并且在体积上也能与传统的保险丝解决方案相匹敌。就像传统的保险丝一样,可以限制故障条件下所产生的危险大电流。然而除此之外,这种PPTC部件还能够在故障消除以及为电路供电的电源重新供电后,直接实现自复能力,从而无需更换熔断的保险丝。     

Manipulating atomic fragmentation processes by controlling the projectile coherence

We have measured the scattering angle dependence of cross sections for ionization in p+H2 collisions for a fixed projectile energy loss. Depending on the projectile coherence, interference due to indistinguishable diffraction of the projectile from the two atomic centers was either present or absent in the data. This shows that, due to the fundamentals of quantum mechanics, the preparation of the beam must be included in theoretical calculations. The results have far-reaching implications on formal atomic scattering theory because this critical aspect has been overlooked for several decades.     

Electrogravitational stability of oscillating streaming fluid cylinder

The electrogravitational instability of on oscillating streaming fluid cylinder under the action of the selfgravitating, capillary and electrodynamic forces has been discussed. The model is governed by the Mathieu second order integro-differential equation. Some limiting cases are recovering from the present general one. The capillary force is destabilizing in a small axisymmetric domain 0<x<1 and stabilizing otherwise. In the absence of electric fields, we found that the model is unstable in a small domain while it is selfgravitating stable in all other domains. The presence of the electric field led to the presence of a great number of stable waves. The electric field has a strong stabilizing influence on the selfgravitating instability of the model. The capillary force has a strong destabilizing influence on the selfgravitating instability of the model.Generally, the uniform stream supports the unstable waves, while the oscillating streaming has stability tendency.