AC Poling study of lead zirconate titanate/vinylidene fluoride-trifluoroethylene composites

It is experimentally known that a polymer matrix phase in a composite of ferroelectric particles dispersed in a ferroelectric polymer can be polarized by using a few cycles of an ac field, without causing much disturbance to the state of polarization of the inclusion particles. This paper attempts to investigate this special poling process for a typical ferroelectric composite system of lead zirconate titanate (PZT) ceramic particles in a vinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) copolymer matrix, upon the application of 10 Hz ac fields of various amplitudes. Compared to a copolymer sample, the composite samples can be polarized at a lower field, and hence show a larger remanent polarization at the same poling field. Among the composites, the observed remanent polarization increases with increasing ceramic volume fraction. These experimental observations can be understood by a simple model, in which space charges are allowed to accumulate at the particle-matrix interfaces because of the electrical conductivity of the constituents. At a fast switching poling field of 10 Hz, the calculation shows that conductivity and charge accumulation effects in the composite are only minimal. Accordingly, although the PZT phase as well as the copolymer phase are both polarized under the ac field, the ceramic phase is only polarized to about 10% when the copolymer phase is almost fully polarized. Thus, one can still use an ac field to polarize only the copolymer phase of the composite without altering the polarization state of the ceramic phase significantly. PACS 77.22.Ej; 77.84.Lf     

Distinguishing between the interior pressures induced from two independent sources within a room using the probabilistic approach

In this paper, a probabilistic approach is introduced and used to distinguish between the interior pressures that are induced from two independent sound sources within a rectangular room. One source is a vibrating wall of the room and the other is an interior point source. The model is set up using the modal analysis method. In the probabilistic method, the probability densities of the uncertain acoustic model parameters are computed. The values of highest probability density are identified and assigned to the uncertain parameters in the acoustic model. The contributions of the sound sources to the total pressure are then obtained from the acoustic model input with the identified parameters. The effects of the modal truncations, the modeling errors, and the measurement locations on the accuracies of the identification process are studied.     

Characterizing the structure of preserved information in quantum processes

We introduce a general operational characterization of information-preserving structures-encompassing noiseless subsystems, decoherence-free subspaces, pointer bases, and error-correcting codes-by demonstrating that they are isometric to fixed points of unital quantum processes. Using this, we show that every information-preserving structure is a matrix algebra. We further establish a structure theorem for the fixed states and observables of an arbitrary process, which unifies the Schr?dinger and Heisenberg pictures, places restrictions on physically allowed kinds of information, and provides an efficient algorithm for finding all noiseless and unitarily noiseless subsystems of the process.     

Properties of a vector soliton laser passively mode-locked by a fiber-based semiconductor saturable absorber operating in transmission

We experimentally demonstrate a passively mode-locked fiber laser employing a fiber-based semiconductor saturable absorber (SSA) operating in transmission. Polarization rotation locked vector solitons are observed in the laser. Due to the intrinsic dynamic feature of the laser, period-doubling of these vector solitons has also been observed. Furthermore, extra spectral sidebands are formed on the optical spectrum, caused by the energy exchange between the two orthogonal polarization components of the vector solitons. By careful reduction of the pump power together with fine adjustment to the cavity birefringence, period-one state can further be obtained. Additionally, the phase noise properties of the vector soliton fiber laser have also been characterized experimentally and analytically.     

Central neurocytoma: typical magnetic resonance spectroscopy findings and atypical ventricular dissemination

PURPOSE: Central neurocytomas (CNCs) are rare neuronal tumors that have a favorable prognosis and lower rate of recurrence compared with other intraventricular neoplasms. Although it may be difficult to distinguish CNC on conventional neuroimaging, typical MR spectroscopy (MRS) features have been reported. We describe the MRI and MRS features of CNC. MATERIALS AND METHODS: Eight patients with CNC were reviewed. Three patients underwent presurgical in vivo single-voxel MRS at short echo time (TE, 35 ms) and multi-voxel MR spectroscopic imaging at long TE (144 ms). The surgically resected tumor specimen of one of these patients was also studied ex vivo using high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance. RESULTS: All eight tumors were located in the lateral ventricles. In six patients, CNC extended into the third ventricle, and in two patients the tumor showed further contiguous intraventricular dissemination into the fourth ventricle. In all three patients who underwent MRS, a characteristic metabolite peak was detected at 3.55 parts per million (ppm) at both long and short TE. HRMAS confirmed the presence of elevated glycine (Gly) at 3.55 ppm, without increase in the concentration of myo-inositol found at the same chemical shift. Elevated choline (at 3.2 ppm) was also seen in all three patients. CONCLUSION: On MRS, CNCs have a typical appearance with a metabolite peak at 3.55 ppm due to increased Gly, and this feature may be helpful in presurgical diagnosis. Although they are rare benign intraventricular tumors, in atypical cases, CNCs can show extensive intraventricular dissemination into the fourth ventricle.     

A novel one-pot pseudo-five-component condensation reaction towards bifunctional diazepine-tetrazole containing compounds: synthesis of 1H-tetrazolyl-1H-1,4-diazepine-2,3-dicarbonitriles and 1H-tetrazolyl-benzo[b][1,4]diazepines

A novel and efficient method has been developed for the one-pot synthesis of bifunctional diazepine-tetrazole containing compounds. 1H-Tetrazolyl-1H-1,4-diazepine-2, 3-dicarbonitrile and 1H-tetrazolyl-benzo[b][1,4]diazepine derivatives were synthesized in good yields using 2,3-diaminomaleonitrile or an aromatic diamine, ketones, trimethylsilyl azide, and an isocyanide in the presence of p-toluenesulfonic acid as a catalyst in methanol at room temperature.