Noise in miniature microphones

The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed.     

Light scattering by critical fluids in the presence of a uniform shear flow

Some predictions are made on dynamic light scattering by critical fluids in the presence of a shear flow. A Doppler shift broadening is predicted to occur whenever the scattering vector has a component along the direction of flow.     

Thermal transport in the hidden-order state of URu2Si2

We present a study of thermal conductivity in the normal state of the heavy-fermion superconductor URu2Si2. Ordering at 18 K leads to a steep increase in thermal conductivity and (in contrast with all other cases of magnetic ordering in heavy-fermion compounds) to an enhancement of the Lorenz number. By linking this observation to several other previously reported features, we conclude that most of the carriers disappear in the ordered state and this leads to a drastic increase in both the phononic and electronic mean free path.     

Evidence for a novel state of superconductivity in noncentrosymmetric CePt3Si: a 195Pt-NMR study

We report on novel antiferromagnetic (AFM) and superconducting (SC) properties of noncentrosymmetric CePt3Si through measurements of the 195Pt nuclear spin-lattice relaxation rate 1/T(1). In the normal state, the temperature (T) dependence of 1/T(1) unraveled the existence of low-lying levels in crystal-electric-field multiplets and the formation of a heavy-fermion (HF) state. The coexistence of AFM and SC phases that emerge at T(N)=2.2 K and T(c)=0.75 K, respectively, takes place on a microscopic level. CePt3Si is the first HF superconductor that reveals a peak in 1/T(1) just below T(c) and, additionally, does not follow the T3 law that used to be reported for most unconventional HF superconductors. We remark that this unexpected SC characteristic may be related to the lack of an inversion center in its crystal structure.     

Use of electron density critical points as chemical function-based reduced representations of pharmacological ligands

In this paper, we propose a reduced representation of molecules of pharmacological interest based on their chemical functions. The proposed representations of the molecules are obtained by a topological analysis of their electron density maps at medium resolution, leading to graphs of critical points. The distribution of the different types of critical points are compared at various levels of resolution for a training set of 22 molecules in order to define the optimal resolution level leading to the best representation of the various chemical functions. The reduced representations can in the future be used for molecular similarity research and pharmacophore proposals.     

Superparamagnetic iron oxide (SPIO) enhancement in the cirrhotic liver: a comparison of two doses of ferumoxides in patients with advanced disease

The aim of this study was to establish whether enhancement of the liver by the MRI contrast agent ferumoxides could be effectively achieved at a reduced dose of 7.5 micromol/kg in patients with advanced liver cirrhosis. Forty-two liver transplant candidates with end-stage cirrhosis underwent SPIO-enhanced MRI at 1.5T, using either 15 micromol/kg or 7.5 micromol/kg ferumoxides. The lower dose of ferumoxides was also used in 21 non-cirrhotic patients with colorectal liver metastases who acted as a control group. The percentage signal intensity loss (PSIL) after SPIO was measured in all patients, and in those patients with tumors the post-SPIO contrast-to-noise ratio (CNR) was measured. The median PSIL after SPIO in the high dose cirrhotic (HDLC), low dose non-cirrhotic (LDNC) and low dose cirrhotic (LDLC) patients was 86.3%, 74.6%, and 64.2% respectively. These differences were significant using the Mann-Whitney U test. Tumors were found in 8 patients in the high dose cirrhotic group, 9 in the low dose cirrhotic group, and all 21 of the control group. No significant differences were found between the CNR values after SPIO in the 3 groups (median values HDLC 15.1, LDNC 23.7, LDLC 19.5). In patients with late-stage cirrhosis the PSIL after SPIO was significantly less at 7.5 micromol/kg than at 15 micromol/kg, but both doses produced a substantial loss of signal. Lesion to liver CNR was not adversely affected by using the lower dose, so when imaging at 1.5T the authors would recommend using 7.5 micromol/kg in patients with liver cirrhosis.     

Angular position of nodes in the superconducting gap of quasi-2D heavy-fermion superconductor CeCoIn5

The thermal conductivity of the heavy-fermion superconductor CeCoIn5 has been studied in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of the thermal conductivity which is characteristic of a superconducting gap with nodes along the ( +/- pi,+/- pi) directions is resolved. The thermal conductivity measurement also reveals a first-order transition at H(c2), indicating a Pauli limited superconducting state. These results indicate that the symmetry most likely belongs to d(x(2)-y(2)), implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity.     

Electro-electrodialysis of HI–I2–H2O mixture using radiation-grafted polymer electrolyte membranes

In the thermochemical water-splitting iodine–sulfur process for hydrogen production, new polymer electrolyte membranes were applied in an electro-membrane process (electro-electrodialysis, EED) to increase the HI molality of HIx solution (HI + I₂ + H₂O mixture) to be over quasi-azeotropic. Radiation grafting of a styrene monomer into a poly(ethylene-co-tetrafluoroethylene) base film and subsequent sulfonation provided electrolyte membranes that had ion exchange capacities (IECs) of 1.1–1.6 mmol/g. With the EED of the HIx solutions using [HI] = [I₂] = 10 mol/kg at 40 °C the transport number of protons, ratio of permeated quantities of water to the protons, and current efficiency all appeared to depend on the IEC of the resulting membranes. When compared to Nafion, the self-made membranes exhibited lower electric cell resistance, and thereby decreasing up to 32% of the overall energy required in the concentration operation.