Statistical solution to the capacity problem in direct-sequence code-division multiple-access communication systems

Tohru Kohda Department of Computer Science and Communication Engineering, Kyushu University, Fukuoka 812-8581, Japan Minoru Tabata Department of Mathematical Sciences, Osaka Prefecture University, Osaka 599-8531, Japan Email: eshima{at}med.oita-u.ac.jp Received on September 21, 2005; Accepted on May 2, 2006 Capacity in the direct-sequence code-division multiple-access(DS/CDMA) communication system was considered according to thecode acquisition performance with the conventional serial-searchmethod, because code acquisition needs a difficult operation.Since capacity in DS/CDMA systems is defined by the maximumnumber of users that can simultaneously transmit their signalswith the same carrier frequencies, assuring a larger capacityis very important in DS/CDMA systems with respect to the economyof frequency source. This paper reconsiders the capacity problemthrough a statistical approach to code acquisition. First, aDS/CDMA system model is reviewed. Second, properties of thecounting method for code acquisition are discussed. It is provedthat the method can acquire the target user's code under anynumber of interference users that simultaneously transmit theirsignals, and that the method can guarantee a considerable precisionin code acquisition. Third, an observation time necessary forcode acquisition is given from a statistical discussion, andthe original counting method is modified into a simpler one.It is concluded that the capacity of the DS/CDMA communicationsystem can be set by the ‘bit error-rate-based capacityor signal-to-noise ratio-based capacity’, i.e. ‘post-acquisition-basedcriterion’, rather than the ‘acquisition-based capacity’.     

Experimental demonstration of spin geometric phase: radius dependence of time-reversal Aharonov-Casher oscillations

A geometric phase of electron spin is studied in arrays of InAlAs/InGaAs two-dimensional electron gas rings. By increasing the radius of the rings, the time-reversal symmetric Aharonov-Casher oscillations of the electrical resistance are shifted towards weaker spin-orbit interaction regions with their shortened period. We conclude that the shift is due to a modulation of the spin geometric phase, the maximum modulation of which is approximately 1.5 rad. We further show that the Aharonov-Casher oscillations in various radius arrays collapse onto a universal curve if the radius and the strength of Rashba spin-orbit interaction are taken into account. The result is interpreted as the observation of the effective spin-dependent flux through a ring.     

Blockade of inflammatory responses by a small-molecule inhibitor of the Rac activator DOCK2

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Highlights? CPYPP binds to DOCK2 DHR-2 domain and inhibits its catalytic activity ? CPYPP inhibits DOCK2-mediated Rac activation in cells ? The structural features of CPYPP required for its inhibitory effect were revealed ? CPYPP inhibits lymphocyte migration and activation in vitro and in vivo     

Relaxation spectrometry in solid polymers based on NMR and EPR measurements

Wide distribution of relaxation times is taken into consideration in determination of the activation energy of the molecular motion associated with the motional narrowings of line widths of magnetic resonance spectra. The molecular motion of rotational vibration around the chain axis of polyethylene in urea-polyethylene inclusion complex is examined. Relaxation spectra can be obtained from the data of the motional narrowings of EPR and NMR by assuming the activation energy as a parameter. Also, the representative relaxation times corresponding to EPR and NMR observations can be estimated. These relaxation times give us an activation energy since EPR and NMR observations correspond to different time constants of observations. The activation energy estimated from the data of the representative correlation times is identical with the activation energy obtained as a parameter in determination of the identical relaxation spectrum from the data of motional narrowings of EPR and NMR observations.     

Strong Inhibitory Effects of Antisense Probes on Gene Expression through Ultrafast RNA Photocrosslinking

We have reported the photochemical regulation of the intracellular antisense effect of antisense probes containing a photo‐responsive artificial nucleic acid, 3‐cyanovinylcarbazole nucleoside (^CNVK). Here we focus on the importance of the photocrosslinking rate on the inhibitory effect on gene expression using photocrosslinkable antisense probes (pcASOs). The inhibitory effect of pcASOs on GFP gene expression was dependent on the photocrosslinking rate of 3‐cyanovinylcarbazole with d ‐threoninol (^CNVD), ^CNVK, or psoralen. The ultrafast RNA photocrosslinking induced the formation of a thermally irreversible covalent bond between pcASOs and the target RNA. These ASOs strongly inhibited gene expression only when the photocrosslinking rate was faster than the random walk of branch migration. In addition, pcASOs containing ^CNVD or ^CNVK targeted the RNAs with secondary structures. These results indicate the regulatory effect of photocrosslinker and photoirradiation energy using pcASOs on the gene expression level.     

A galvanic solid-state sensor for monitoring ozone and nitrogen dioxide

The sensor is based on silver and platinum electrodes with an intervening silver iodide disk as a solid electrolyte. The small disk (13 mm diameter) is easily made by pressing (7000 kg cm^-2) silver powder, silver iodide and a platinum gauze in layers in a die. The detector cell containing the disk is thermostated at 120 ± 0.1°C. When sample gas at 30 ml min^-1 impinges on the platinum cathode, the current flowing in the external circuit is linearly related to the concentration of ozone and/or nitrogen dioxide up to 0.5 ppm from the detection limit of 0.5 ppb for ozone or 1 ppb for nitrogen dioxide.     

Proposed structure of the cyclic peptide dolastatin 3, a powerful cell growth inhibitor,should be revised!

The cyclic peptide proposed for the structure of the powerful cell growth inhibitory dolastatin 3, its diastereomers, and their isomers on the reverse order have been synthesized by the use of diphenyl phosphorazidate(DPPA) and diethyl phosphorocyanidate(DEPC). Their physicochemical and biological properties have shown that the proposed structure is untenable.