High Gain Level Research Articles

Assessing baroreflex sensitivity by the transfer function method: what are we really measuring?

by governing the autonomic outflow to the heart and blood vessels, arterial baroreceptors play a central role in controlling short-term blood pressure responses to the hemodynamic perturbations continuously occurring in daily life. Abnormalities in baroreflex function are thought to play an

WIDEBAND CAVITY-BACKED PATCH ANTENNA FOR PCS/IMT2000/2.4 GHZ WLAN

Abstract—A wideband cavity-backed patch antenna is presented for operating at PCS, IMT200, and 2.4 GHz WLAN bands. A parasitic patch and a probe with a capacitor patch is used to enhance the bandwidth. The cavity-backed and without cavity-backed antenna has been compared. It has been found that the cavity backed antenna has wide impedance bandwidth of 43% and high gain level. It can simultaneously serve most of the modern wireless communication applications that operate at 1.7 GHz–2.5 GHz.

Open-canal fittings

Fitting hearing aids involves innovation and compromise. This is especially true in deciding the tightness of the fit, whether of an earmold or a custom product. Tight-fitting instruments are good for obtaining high levels of gain and output, especially in the lower frequencies, and for minimizing feedback problems. However, they often are uncomfortable, sometimes create an unacceptable occlusion effect, and can give the patient a “plugged up” sensation. If the patient has normal or near-normal hearing in the lower frequencies, it is common practice to move toward a more open fitting to alleviate occlusion and let low frequencies into the ear naturally. In this case, the compromise is reduced gain and output, and a greater chance of unwanted acoustic feedback. There is little documentation of the first open-canal (OC) fittings, but we know they received considerable attention immediately after the CROS-type hearing aid was introduced.1 It was quickly discovered that the open earpieces (or tubing only) used for the CROS hearing aid also could be used for ipsilateral high-frequency amplification (hence, the term IROS [ipsilateral routing of signals], referring to a large vent). In the late 1960s, researchers showed that OC fittings could provide useful high-frequency amplification.2-4 In the ensuing decades, there wasn’t much excitement about open fittings, though there was some renewed interest during the Libby horn’s peak of popularity5 and on other occasions when a product designed specifically for high-frequency hearing loss was introduced.6 The ho-hum attitude toward OC fittings that persisted for more than 30 years was stirred up considerably a few years ago when five key aspects were combined in a single OC product: a small “cute” BTE casing, multichannel compression and gain adjustments, a thin tube channeling the sound from the hearing aid to the ear, a comfortable nonoccluding eartip, and, most importantly, effective feedbackreduction algorithms. As reviewed by Mueller,7 these five factors combine to offer a wide range of potential patient benefits, and OC products have rapidly taken over a sizable share of the total hearing aid market. While the peer-reviewed journals have published little about these modern OC fittings, several articles about this style have appeared in the trade journals, and the OC product is a hot topic at hearing aid workshops and seminars. However, there are still some key issues related to these products that need further clarification, and maybe even a couple areas where misconceptions exist. In this paper, we’ll provide some tips on OC fittings, which we hope will clarify more than they confuse.

A Review and Analysis: Does Amplification Experience Have an Effect on Preferred Gain Over Time?

There is a widespread belief among practising audiologists that new users of hearing aids prefer lower gain levels than experienced hearing aid users and that new users will gradually come to prefer higher gain levels over time. A review of 14 papers was conducted to determine the validity of this belief and the data from three of the studies (Cox & Alexander, 1992; Horwitz & Turner, 1997; Humes et al., 2002) were then examined in closer detail. The audiometric data for 175 subjects, for whom use gain was measured at various intervals postfitting, was divided into 'new' (N = 98) and 'experienced' (N = 77) groups. For each of these subjects, the NAL-R target was calculated and the prescribed gain was compared to the use gain. An analysis of these data, along with the conclusions of the other papers reviewed here, suggests that there is no significant difference between the gain preferences of new and experienced hearing aid users, nor do the gain preferences of new users change over the first 12 months of hearing aid use.

Analysis of evolution of exon-intron structure of eukaryotic genes

The availability of multiple, complete eukaryotic genome sequences allows one to address many fundamental evolutionary questions on genome scale. One such important, long-standing problem is evolution of exon-intron structure of eukaryotic genes. Analysis of orthologous genes from completely sequenced genomes revealed numerous shared intron positions in orthologous genes from animals and plants and even between animals, plants and protists. The data on shared and lineage-specific intron positions were used as the starting point for evolutionary reconstruction with parsimony and maximum-likelihood approaches. Parsimony methods produce reconstructions with intron-rich ancestors but also infer lineage-specific, in many cases, high levels of intron loss and gain. Different probabilistic models gave opposite results, apparently depending on model parameters and assumptions, from domination of intron loss, with extremely intron-rich ancestors, to dramatic excess of gains, to the point of denying any true conservation of intron positions among deep eukaryotic lineages. Development of models with adequate, realistic parameters and assumptions seems to be crucial for obtaining more definitive estimates of intron gain and loss in different eukaryotic lineages. Many shared intron positions were detected in ancestral eukaryotic paralogues which evolved by duplication prior to the divergence of extant eukaryotic lineages. These findings indicate that numerous introns were present in eukaryotic genes already at the earliest stages of evolution of eukaryotes and are compatible with the hypothesis that the original, catastrophic intron invasion accompanied the emergence of the eukaryotic cells. Comparison of various features of old and younger introns starts shedding light on probable mechanisms of intron insertion, indicating that propagation of old introns is unlikely to be a major mechanism for origin of new ones. The existence and structure of ancestral protosplice sites were addressed by examining the context of introns inserted within codons that encode amino acids conserved in all eukaryotes and, accordingly, are not subject to selection for splicing efficiency. It was shown that introns indeed predominantly insert into or are fixed in specific protosplice sites which have the consensus sequence (A/C)AG|Gt.

Detection of weak magnetic fields propagated through a ferrous steel boundary using a super narrowband digital filter

An instrumentation system is described that is capable of launching high frequency magnetic fields through a large mild steel plate 2 mm in thickness, and detecting them on the face opposite to the transmitter with remarkable signal to noise ratios. Results for signal frequencies ranging between 4.5 kHz and 13 kHz are reported. The skin depth at 9 kHz, for the steel used, is approximately 137 μm. The detection of the minute fields arriving at the receiving coil is made possible by the use of digitally synthesized input signals, low-noise amplification, and in particular the use of a real time digital signal processing system that isolates the signal of interest using a super-narrowband IIR filter and very high levels of distortion-free gain. Although traditional methods of weak signal detection, such as lock-in amplification, may also be applied in this context, the digital approach discussed here is both more cost effective and flexible, allowing the simultaneous detection of multiple frequencies.

High-gain omnidirectional printed collinear antenna

A printed collinear antenna with a narrow (10 mm) width showing high-gain omnidirectional radiation is presented. The antenna comprises three half-wavelength elements of one strip dipole, one meandered line, and one straight strip connected in series, and has a total height of only 113.5 mm (about 92% wavelength of the frequency at 2442 MHz) for operation in the 2.4-GHz WLAN band. Due to the meandered line, in which the excited surface current has a phase opposite to that of the strip dipole and straight strip, the destructive radiation in the azimuthal plane for the antenna is suppressed. Conversely, the strip dipole and straight strip are constructive with regard to radiation, which leads to high-gain omnidirectional radiation for the antenna. A prototype showing good omnidirectional radiation (with gain variations less than 1.5 dB in the azimuthal plane) with a high gain level of about 4.4 dBi across the 2.4-GHz WLAN band is presented. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 348–351, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20631

Molecular homogeneity in erbium-doped sol-gel waveguide amplifiers

High net gain levels have recently been reported in silica-on-silicon waveguide amplifiers, using the sol-gel method of glass deposition. Spectroscopic measurements indicate that high inversion levels are achieved at high erbium concentrations, suggesting a high uniformity in the erbium distribution. Here we show that high inversion and low scattering losses are only achieved in sol-gel waveguides which have had restricted heat treatment and that both degrade upon additional annealing. Evolution of scattering loss spectra are presented, and these are included in a model of the ytterbium-sensitized waveguide amplifiers to show that the gain reduction with heat treatment is not wholly due to pump and signal excess losses, but also to changes in the spectroscopic properties of the erbium ions. In particular, the formation of clusters in which inversion is rapidly quenched is indicated. Thus, we show that the superior performance of the sol-gel method for rare-earth doping of silica waveguides, for amplifier and laser applications, results from its ability to form homogenous molecular structures which are meta-stable and which consequently cannot be formed in glasses that require high-temperature consolidation or annealing.

Letter-Sound Correspondence Acquisition in First Semester Russian

Although teachers of first year Russian courses know that students often mistake letters of the Cyrillic alphabet for English letters when reading aloud and writing, no studies have documented which letters cause the most frequent misreadings, how long misreading persists, and what implications misreading has for student achievement. This semester-long study attempts to answer these questions by isolating the question of letter-sound correspondence from the larger questions of the students’ interlanguage phonology. The researchers found that ц, ё, ю, й, э consistently gave students difficulty. After 12 weeks (84 hours) of instruction, students had 93% accuracy in matching Cyrillic letters to their primary sound values. While this represents a high degree of accuracy by the end of the first semester, the researchers found that higher accuracy rates earlier in the semester (after 4 weeks [28 hours] of instruction) had a moderate positive correlation with success in the course (as measured by final grade), while high levels of gain in accuracy between the fourth and twelfth weeks of the semester showed moderate negative correlation with success in the course, suggesting that the earlier the students master letter-sound correspondences, the greater their chances for success in studying other features of the language.

WDM transmission over multiple long spans with bidirectional Raman pumping

We investigate the feasibility of WDM transmission over multiple spans that are twice as long as those typically used in commercial systems. Using longer spans reduces the number of repeater sites, potentially lowering the operating costs of medium- and long-haul terrestrial systems. We show that bidirectional Raman pumping is a key enabling technology. In particular, we demonstrate the benefits of high levels of codirectional Raman gain, up to 10-dB more than is used in transmission experiments with standard span lengths. Then, we transmitted 40 /spl times/ 10.66 Gb/s with uncorrected bit-error ratios better than 10/sup -9/ using 200-km spans of nonzero dispersion fiber with 14.5-dB of Raman co-gain over a reach of 2400 km. We also measured the maximum amount of span loss that was tolerable for a given system reach for 200-km span transmission at 10 Gb/s. After optimization at twelve distances (800 to 3000 km), we found that the tolerable span loss increased by 1 dB for each 200-km reduction in reach.

Metal-plate 1×2 array antenna for 5.2/5.8 GHz WLAN operation

A novel metal-plate 1×2 array antenna constructed easily from a single metal plate and suited for WLAN operation in the 5.2/5.8 GHz bands (5150–5350/5725–5875 MHz) is presented. The metal-plate array antenna comprises two radiating elements series-fed by a 50 Ω microstrip line and excited in phase, leading to a high antenna gain level (>4.0 dBi) for frequencies across the 5.2/5.8 GHz WLAN bands.

Theory of optical near-resonant cone emission in atomic vapor

A time-dependent theory for conical emission during near-resonant propagation of laser light in an atomic vapor, which includes full propagation for the laser and frequency sidebands in a nonlinear two-level medium is presented. The density-matrix equations for the dipole moment and population are solved in the dressed atomic frame. The polarization source terms are accurate to order {gamma}/R, where {gamma} is a damping constant and R is the generalized Rabi frequency. Analytical plane-wave solutions and numerical, cylindrically symmetric propagation simulations including diffraction are presented. It is shown that the calculations with cylindrically symmetric fields and atomic excitation profiles are incapable of accounting for the high levels of optical gain that are responsible for the intense conical emission observed in experiments. This result is at first surprising, since the model accounts rigorously for all of the physical phenomena that have been previously proposed as being responsible for generating large gains, and the calculation matches the symmetry of the observations. The lack of large calculated gain seems to imply the existence of higher-order (m>0) radial modes in the field for the experimental conditions that give rise to cone emission. In the simulations, however, the cylindrically symmetric fields do produce weak red-detuned conesmore » with angular-frequency distributions similar to those seen in experiments.« less

Time-dependent structure in the discharge rate of human motor units.

The aim of this study was to examine the influence of visual and motor processes on the deterministic and stochastic structure of force output and motor unit discharge variability. Young adult subjects produced continuous, isometric force at 3, 6, 12, and 24% of their maximal voluntary contraction at low and high visual gain levels through abduction of the index finger. Force and fine-wire intramuscular electromyography were recorded. There was a linear increase in discharge irregularity with increases in the mean motor unit discharge rate (8-30 Hz). Recurrence analysis showed that the percentage of deterministic structure in discharge variability remained high, but decreased linearly with increased motor unit discharge rate. Surrogate analyses confirmed that the motor unit discharge variability was inconsistent with an uncorrelated and linearly correlated Gaussian noise process. Spectral analysis revealed that both the force output and the mean time-varying motor unit discharge time series had a dominant frequency of 0-2 Hz. Visual feedback gain did not affect the individual motor unit discharge patterns. The motor unit discharge rate has deterministic time-dependent structure. The motor unit discharge rate is modulated at multiple time scales likely by pre- and post-synaptic induced fluctuations from spinal level pathways impinging on the motor neuron.

Wideband and high-gain one-patch microstrip antenna coupled with H-shaped aperture

The design, fabrication, and experimental implementation of the one-patch microstrip antenna coupled with an H-shaped aperture are presented. The presented antenna has a wide bandwidth, high gain, and low cross-polarisation levels with only one-patch. The measured bandwidth of this antenna is 56.2% for the voltage standing wave ratio /spl les/2.0. The cross-polarisation level is below -18.2 dB at the E-plane and below -25.7 dB at the H-plane. The maximum gain at 2.05 GHz is 10.4 dBi and the 3 dB gain bandwidth with a centre frequency at 2.17 GHz is 24%.

Crosslinking Analysis of Polycarboxylic Acid Durable Press Finishing of Cotton Fabrics and Strength Retention Improvement

Cotton fabric is treated in different concentrations of BTCA and SHP solutions. The fabric weight gain is confirmed by FTIR analysis, and the peak ratio of 1720 cm-1/1380 cm-1 has a good linear relation with fabric weight gain. The results show that BTCA is most effective for durable press finishing at around 2%. The moisture regain of the treated fabric decreases as the weight gain increases before 10%, and then increases at high levels of weight gain. These results indicate that except for inter- and intramolecular crosslinking, some side grafts are formed during the treatment, and at BTCA high concentrations, the quantity of side grafts increases. When the fabric is cured in tension, the intramolecular crosslinks can be reduced and the treated fabric's strength retention can improve from 45% to above 75%.

Optimising the electronic and optoelectronic properties of thin-film diamond

Abstract The realisation of effective UV photodetectors from thin-film diamond requires the selection of good-quality substrate material and careful device design. However, these alone are insufficient to yield high-performance characteristics: post-growth treatments are required to modify the optoelectronic properties of the diamond. Photoconductive devices fabricated in this way can be truly blind to visible light, fast and offer high levels of photoconductive gain. The origin of these improvements has been studied using thermally stimulated current (TSC) and photoconductivity measurements. The treatments used appear to provoke extremely high carrier lifetimes, encouraging high gain whilst eradicating extrinsic photoconduction. TSC reveals that a new trap state is introduced at (Ea≈0.6 eV). A model to explain the changes in device characteristics is discussed.

A digital frequency-domain implementation of a very high gain hearing aid with compensation for recruitment of loudness and acoustic echo cancellation

People with loudness recruitment have a compressed dynamic range between the sound-pressure levels corresponding to threshold and discomfort. This highly frequency-dependent phenomenon requires a nonlinear filter for compensation. To achieve the high levels of gain required for profound hearing impairment, the hearing aid must also be capable of canceling the ever present acoustic feedback. This paper describes a digital hearing aid, realized in the frequency domain, that compensates for recruitment of loudness and cancels echos. The DFT-based approach permits the use of fast and computationally efficient algorithms for the nonlinear compensation and adaptive FIR filtering. The echo canceler is adapted using only the available (e.g. speech) input signal. An analysis is presented of the closed-loop hearing aid system and the adaptive adjustment law. The problems resulting from the use of a nonlinear hearing-loss compensator and stability problems caused by a rapidly changing echo path are discussed. The proposed solutions have been implemented and tested on a dummy head using a behind-the-ear hearing-aid device. The result is a device that runs more than 20 dB above the critical gain without any audible artifacts.

Signal recovery using a cascade adaptive filter: application to ultrasonic testing of heterogeneous media

The basic principles of an adaptive filter implemented in discrete space are discussed, and an algorithm for a two-stage cascade adaptive filter using the least-mean-squares method is given. The filter was employed to process digitised low-frequency ultrasonic signals propagated through concrete, obtained under a variety of transducer/sample coupling conditions. Very significant levels of signal recovery were possible with waveforms initially exhibiting poor signal-to-noise ratios arising from high levels of amplifier gain.

Mode-locking at very high repetition rates more than terahertz in passively mode-locked distributed-Bragg-reflector laser diodes

We propose a technique for achieving mode-locking at very high repetition rates more than terahertz with high output power using a distributed-Bragg-reflector (DBR) laser, including an intracavity saturable absorber. This method is based on harmonic passive mode-locking at high gain levels and the selectivity of harmonic numbers related to the spectrum-filtering property of the intracavity Bragg reflector. Transform-limited pulses at repetition rates from 500 GHz to 1.54 THz were generated with an output power exceeding 15 mW. We studied stability of harmonic pulses by using conventional self-consistent mode-locking equations. We also discuss the effect of the spectrum-filtering properties of the intracavity Bragg reflector to the characteristics of mode-locked pulses.

Experimental and theoreticalinvestigations of new compact largebandwidth aperture-coupled microstripantenna

The authors propose an efficient amelioration of the concept of large bandwidth aperture-coupled microstrip antennas by coupling a CPW line-fed slot to a microstrip antenna. The CPW-fed aperture-coupled microstrip antenna investigated has a large bandwidth with high gain and low crosspolarisation levels, is compact with only one substrate, and may be easily connected to both passive and active components. A numerical model has been developed and the theoretical results are in good agreement with the experiments.