Properties and Applications of Varistor–Transistor Hybrid Devices

The nonlinear current–voltage characteristics of a varistor device are modified with the help of external agents, resulting in tuned varistor–transistor hybrid devices with multiple applications. The substrate used to produce these hybrid devices belongs to the modified iron titanate family with chemical formula 0.55FeTiO₃·0.45Fe₂O₃ (IHC45), which is a prominent member of the ilmenite–hematite solid-solution series. It is a wide-bandgap magnetic oxide semiconductor. Electrical resistivity and Seebeck coefficient measurements from room temperature to about 700°C confirm that it retains its p-type nature for the entire temperature range. The direct-current (DC) and alternating-current (AC) properties of these hybrid devices are discussed and their applications identified. It is shown here that such varistor embedded ceramic transistors with many interesting properties and applications can be mass produced using incredibly simple structures. The tuned varistors by themselves can be used for current amplification and band-pass filters. The transistors on the other hand could be used to produce sensors, voltage-controlled current sources, current-controlled voltage sources, signal amplifiers, and low-band-pass filters. We believe that these devices could be suitable for a number of applications in consumer and defense electronics, high-temperature and space electronics, bioelectronics, and possibly also for electronics specific to handheld devices.     

Robust MIMO H∞ Integral-Backstepping PID Controller for Hovering Control of Unmanned Model Helicopter

The problem of stabilization of a model helicopter in a hover configuration subject to parametric uncertainty and external disturbances is addressed. Multiinput multioutput (MIMO) proportional-integral-derivative (PID) control law is reformulated into a full-state feedback control law to synthesize the controller by using robust H∞ control theory. In full-state feedback representation, PID control has implicit integral-backstepping structure. Therefore a new parameter, ρ, can be introduced that acts on the derivative of the control signal. The parameters of MIMO PID controller are then obtained with solving the algebraic Riccati equation with selecting the values of ρ and γ. Model helicopter simulation is carried out to verify the performance of the proposed controller to stabilize the uncertain helicopter model and to suppress external disturbances.     

A Practical-Time Related-Key Attack on the KASUMI Cryptosystem Used in GSM and 3G Telephony

Over the last 20 years, the privacy of most GSM phone conversations was protected by the A5/1 and A5/2 stream ciphers, which were repeatedly shown to be cryptographically weak. They are being replaced now by the new A5/3 and A5/4 algorithms, which are based on the block cipher KASUMI. In this paper we describe a new type of attack called a sandwich attack, and use it to construct a simple related-key distinguisher for 7 of the 8 rounds of KASUMI with an amazingly high probability of 2^?14. By using this distinguisher and analyzing the single remaining round, we can derive the complete 128-bit key of the full KASUMI with a related-key attack which uses only 4 related keys, 2²⁶ data, 2³⁰ bytes of memory, and 2³² time. These completely practical complexities were experimentally verified by performing the attack in less than two hours on a single-core of a PC. Interestingly, neither our technique nor any other published attack can break the original MISTY block cipher (on which KASUMI is based) significantly faster than exhaustive search. Our results thus indicate that the modifications made by ETSI’s SAGE group in moving from MISTY to KASUMI made it extremely weak when related-key attacks are allowed, but do not imply anything about its resistance to single-key attacks. Consequently, there is no indication that the way KASUMI is implemented in GSM and 3G networks is practically vulnerable in any realistic attack model.     

Adaptive finite element analysis of axisymmetric freezing

The paper describes an adaptive finite element analysis of the transient axisymmetric freezing process. Adaptivity schemes are applied to both space and time tessellations. Error equidistribution adjusts the nodal positions and Taylor series analysis of time truncation error selects the time step. In implicit time integration, the location of the freezing front and the nodal temperatures at the next time is solved by full Newton all at once. The method appears to be accurate; in cases for which closed-form solutions are available, it agrees well with them. It also avoids the problem found in the Modified Isotherm Migration Method where the freezing front tends to retrogress when solid just forms on the outer surface cooled by convection.     

Immobilization of Co(III) using tethered cyclam ligand on SBA-15 mesoporous silica for aerial oxidation of ethylbenzene

Cyclam type macrocyclic ligand was tethered onto mesoporous silica surface through N-functionalization of the cyclam. The mesoporous silica was synthesized directly with in-built chloropropyl functional group by applying microwave synthesis approach and the cyclam ligand was tethered via the surface substitution reaction of the chloro group. The tethered cyclam ligand was proven to facilely accommodate Co(III) cation into its cavity. This Co(III)cyclam-functionalized mesoporous silica showed good catalytic activity in the aerial oxidation of ethylbenzene to give acetophenone as the major product, which exceeded 60%. The presence of pyridine ligand which bounded to the axial sites of the tethered Co(III)cyclam complex enhanced the activity of the catalyst with sustaining the selectivity.     

Computing Derivatives of Noisy Signals Using Orthogonal Functions Expansions

In many applications noisy signals are measured. These signals have to be filtered and, sometimes, their derivative has to be computed. In this paper a method for filtering the signals and computing the derivatives is presented. This method is based on expansion onto transformed Legendre polynomials. Numerical examples demonstrate the efficacy of the method as well as the theoretical estimates. This research was supported by the ISRAEL SCIENCE FOUNDATION (grant No. 1364/04) and the UNITED STATES-ISRAEL BINATIONAL SCIENCE FOUNDATION (grant No. 2004099).     

Probabilistic power system production cost and reliabilitycalculation by the Z-transform method

The authors describe a novel method of probabilistic power system production cost and reliability calculation using the Z transform. In the proposed method, the generating unit available capacity probability density functions (PDFs) are represented by probability impulses. These PDFs are convolved using the Z transform to produce equivalent capacity PDFs. By operating the equivalent capacity PDFs on the system demand, the unit energies, loss of load probability (LOLP), and expected unserved energy (EUE) can be calculated for each load level and the total demand. The method is compared with the cumulant method and Calebrese's traditional direct convolution procedure in terms of accuracy and computing time using the IEEE Reliability Test System. The main advantage of the new method is that actual load and generator availability data can be used directly, rather than via a mathematical representation such as cumulants. An efficient recursive algorithm using the Z transform procedure has been formulated to allow fast evaluations of convolution and deconvolution of PDFs. In terms of computing time, the new method is not much slower than the cumulant method. LOLP and EUE are also calculated more accurately