Improved Bounds for Wireless Localization

We consider a novel class of art gallery problems inspired by wireless localization that has recently been introduced by Eppstein, Goodrich, and Sitchinava. Given a simple polygon P, place and orient guards each of which broadcasts a unique key within a fixed angular range. In contrast to the classical art gallery setting, broadcasts are not blocked by the edges of P. At any point in the plane one must be able to tell whether or not one is located inside P only by looking at the set of keys received. In other words, the interior of the polygon must be described by a monotone Boolean formula composed from the keys. We improve both upper and lower bounds for the general problem where guards may be placed anywhere by showing that the maximum number of guards to describe any simple polygon on n vertices is between roughly \frac35n\frac{3}{5}n and \frac45n\frac{4}{5}n . A guarding that uses at most \frac45n\frac{4}{5}n guards can be obtained in O(nlog n) time. For the natural setting where guards may be placed aligned to one edge or two consecutive edges of P only, we prove that n−2 guards are always sufficient and sometimes necessary.     

Preparation of niobium oxide films as a humidity sensor

Niobium oxide films were prepared over a quartz plate by withdrawing it from a solution of niobium penta-isopropoxide (NIP) dissolved in sec-propyl alcohol. The films calcined at 673 K were well controlled in the film thickness either by NIP concentration in the solution or by the withdrawing rate of the quartz plate from the solution. BET surface area of the calcined films was as huge as around 400 m²g₋₁ and was not reduced by cyclic adsorption/desorption of water vapor. A rapid decrease and increase in the electrical resistivity of the calcined films was well associated with the cyclic adsorption/desorption of water vapor. The decrease in the electrical resistivity of the films by water vapor adsorption was more than 10 times sensitive than the decrease caused by the adsorption of ethanol, hydrocarbons, carbon monoxide and carbon dioxide. These results suggest an application of the niobium oxide films as an element of a humidity sensor.

The calcined films were proved by SEM observation to consist of tiny particles possessing a lotofmicropores sized less than 20 A. The decrease in the electrical resistivity of the films, or the increase in the electrical conductivity, was attributed to the water vapor adsorbed in these micropores. In order to identify the charge carriers during water vapor adsorption on the films, changes in the impedance and the phase shift caused by water vapor adsorption were measured using an LCR meter in AC frequency range of 10 Hz to 100 kHz. From a complex impedance plotting, single semicircule was obtained for water vapor adsorption onto the films, suggesting single adsorbed species as a charge carrier. Assuming an equivalent electric circuit for the films adsorbing water vapor, a constant capacitance was calculated under various partial pressures of water vapor, probably suggesting that the charge carriers will be H₃O⁺ on the films.     

A current sensorless MPPT control method for a stand‐alone‐type PV generation system

In this paper, a current sensorless MPPT control method for a stand‐alone‐type PV generation system is proposed. This control method offers advantages of the simplified hardware configuration and low cost by using only one sensor to measure the PV output voltage. When used as a stand‐alone‐type with a battery load, the experimental results show that the estimated values of PV output current are accurate, and the use of the proposed MPPT control increases the PV generated energy by 16.3% compared to the conventional system. Furthermore, the authors clarified that the proposed method has an extremely high UUF (useful utilization factor) of 98.7%. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 65– 71, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20424     

Parallel processing for multiplication modulo by means of phase modulation

We apply optical parallel processing to operations for multiplication modulo, which is one of the key components of a factorization algorithm. With this method, optical phase modulation provides the results of modulo operations. We construct a prototype system based on a Michelson interferometer with a photodetector array. Mirrors are set at both object and reference arms to generate interference fringes. A mirror in the object arm is tilted slightly, whereas the reference arm is set perpendicular to the optical axis. The tilt angle is determined by parameters for the target modulo operations. The presented system can achieve massive data processing in parallel with only simple implementation. We present our experimental results to verify the usefulness of our method.     

In vivo and in vitro blood compatibility of polyelectrolyte complexes formed between cellulose derivatives

The blood compatibility of cellulosic polyelectrolyte complexes (PECs) and the effect of excess charge in PEC on the blood compatibility were examined in detail by both in vivo and in vitro blood tests. For this purpose, two types of quaternary ammonium cellulose derivatives were prepared by treating cellulose or hydroxyethyl cellulose with glycidyl trimethylammonium chloride. In vivo blood tests were made by implanting the polymer-coated suture into a jugular and femoral vein of a dog. In vitro blood tests include the measurement of whole blood coagulation time on polymer-coated glass tubes, platelet adhesion measurements using a column packed with polymer-coated glass beads, and a measurement of activation of the intrinsic coagulation system. It was found that among the PECs examined, the PECs containing quaternary ammonium derivatives as polycation components have an excellent blood compatibility. The experiments on the effect of excess charge in PEC revealed that (i) the relative coagulation time of whole blood is almost independent of the mole ratio of polycation to polyanion component within the mole ratios examined, being in good agreement with those by in vivo blood tests, but (ii) platelet adhesion increases with increasing the mole ratio of polycation/polyanion in the PEC, and (iii) the activation of the intrinsic coagulation system increases with decreasing the mole ratio.     

Thermotropic cellulose derivatives with flexible substituents

Summary Three kinds of fully substituted cellulose derivatives, cellulose triheptanoate (CTH), tri-O-heptyl cellulose (THC) and tri-O-2-butoxyethyl cellulose (TBC) were prepared. These polymers, having a side chain of similar length but of differing chemical structure, were found to show significantly different therraotropic behavior: TBC forms a cholesteric liquid crystalline phase at temperatures between 50 °C and 165 °C, the cholesteric pitch covering the region of visible lights. THC also displays a cholestric structure at temperatures between 80 °C and 130 °C with pitches on the order of several micrometers. CTH appears to show liquid crystallinity only in a very limited temperature range around 100 °C.     

Optimization algorithm for <Emphasis Type="Italic">k</Emphasis>-anonymization of datasets with low information loss

Anonymization is the modification of data to mask the correspondence between a person and sensitive information in the data. Several anonymization models such as k-anonymity have been intensively studied. Recently, a new model with less information loss than existing models was proposed; this is a type of non-homogeneous generalization. In this paper, we present an alternative anonymization algorithm that further reduces the information loss using optimization techniques. We also prove that a modified dataset is checked whether it satisfies the k-anonymity by a polynomial-time algorithm. Computational experiments were conducted and demonstrated the efficiency of our algorithm even on large datasets.     

Lyotropic mesophase formations of HPC/imogolite mixture

Summary The mesophase formation was observed from the system of mixed organic polymer (hydroxypropyl cellulose) and inorganic polymer (imogolite) in acetic acid aqueous solution. The phase diagram of the mesophase formation was drawn as a function of imogolite content. The mesophase structure was found to change from the helicoidall arrangement of nematic sheets to the pile of pleated nematic sheets with increasing imogolite content.     

On listing,sampling, and counting the chordal graphs with edge constraints

We discuss the problems to list, sample, and count the chordal graphs with edge constraints. The objects we look at are chordal graphs sandwiched by a given pair of graphs where we assume that at least one of the input graphs is chordal. The setting is a natural generalization of chordal completions and deletions. For the listing problem, we give an efficient algorithm running in polynomial time per output with polynomial space. As for the sampling problem, we give two clues that indicate that a random sampling is not easy. The first clue is that we show #P-completeness results for counting problems. The second clue is that we give an instance for which a natural Markov chain suffers from an exponential mixing time. These results provide a unified viewpoint from algorithms’ theory to problems arising from various areas such as statistics, data mining, and numerical computation.     

Formation of polyelectrolyte complexes between cellulose derivatives and their blood compatibility

Formation of polyelectrolyte complexes (PECs) between cellulose derivatives in aqueous solution and their blood compatibility were examined. To this end, two types of quaternary ammonium cellulose derivatives, Q-Cell and Q-HEC, were prepared by treating cellulose and hydroxyethyl cellulose (HEC), respectively, with glycidyl trimethylammonium chloride. Anionic derivatives were carboxymethyl cellulose (CMC) with different degrees of substitution (DS) and cellulose sulfate (CS). In vivo blood tests were made by a method of peripheral vein indwelling suture. The results showed that the complex formation of Q-Cell did not follow a stoichiometric reaction, but Q-HEC reacted stoichiometrically with CMC and CS. It was also found that water-insoluble cellulosic PECs are soluble in formic acid, showing that the cellulosic PEC films can be prepared from formic acid solutions. The blood tests revealed that by the criteria of the test method employed in this work, cellulosic PECs had a good blood compatibility.