Effects Of Frequency Differences Research Articles

Second-order near trapping of water waves by a square array of vertical columns in bi-chromatic seas

Near trapping of water waves by an array of closely spaced columns is a hydrodynamic phenomenon with practical applications. A numerical investigation is conducted for the second-order interaction of bi-chromatic waves with a square array of vertical columns. The cross-sectional shape of the columns can be either circular or square with rounded corners. Numerical results indicate that a four-column cluster can amplify free-surface elevation through a near-trapping mechanism. Three lower-order near-trapped modes, namely p=0, 2 and 3 modes, are primarily concerned, among which the amplification corresponding to the p=2 mode is most pronounced. In addition, the four-column cluster can create both the linear and second-order near trappings. The latter could occur when the frequency sum of a pair of incident waves is consistent with the near-trapping frequency. The linear and second-order near-trapped modes own common characteristics. The second-order near-trapping response is predominated by the ‘potential wave’ component, while the ‘quadratic wave’ component plays a secondary role. Meanwhile, the effect of frequency difference on the mode shape in the second order is not evident. It is also noted that a decrease in the corner ratio can enhance the hydrodynamic interference effect among the columns and, in turn, evidently promote the near-trapping response for the p=2 mode. An approximate approach is developed for the second-order near-trapping response, in which the ‘quadratic wave’ component is evaluated exactly. In contrast, the complicated ‘potential wave’ component corresponding to a pair of incident waves with distinct frequencies is approximated by that in mono-chromatic seas with the mean frequency. This approach is based on the hypothesis of weakly scattering of linear wave fields. Numerical results indicate that such approximation offers a reasonable alternative for the near-trapped modes in the low-frequency region.

EFFECT OF THE DIFFERENCE IN SOUND WAVE-BASED ATTRACTOR FREQUENCY ON THE CATCH OF HALFBEAK FISH (OXYPOHAMPHUS MICROPTERUS) USING TRAMMEL NET AT SURABAYA COAST.

The purpose of this study was to determine the effect of differences in frequency of sound wave-based attractors on the catch of halfbeak fish (oxyporhamphusmicropterus) on a three-layer trammel net on

Effect of frequency difference on sensitivity of beats perception

Two vibrations with slightly different frequencies induce the beats phenomenon. In tactile perception, when two pins of different frequencies stimulate the fingertips, an individual perceives a beats caused by a summation stimulus of the two vibrations. The present study demonstrates experimentally that humans can perceive another vibration based on the beats phenomenon when two tactile stimuli with slightly different frequencies are stimulated on the finger pad with a small contactor in different locations at the same time. Moreover, we examined the amplitude of the detection threshold to be able to perceive beats phenomenon on the index finger with 5 carrier frequency (63.1, 100, 158.5, 251.2, and 398.1 Hz) and 4 beats frequency (2.5, 3.98, 6.31, and 10 Hz) when two stimuli 1 mm distance apart are vibrated at a slightly different frequency. From the experiments, it is concluded that the amplitude threshold to be able to perceive beats decreases as the standard frequency increases under 398 Hz. Furthermore, from comparing the absolute detection threshold and beats detection threshold, as the carrier frequency increases, the required amplitude at two pins for the detection of beats decreases compared to absolute vibration.

Assessing the relative importance of dispersal in plant communities using an ecoinformatics approach

Increased insight into the factors that determine the importance of dispersal limitation on species richness and species composition is of paramount importance for conservation and restoration ecology. One way to explore the importance of dispersal limitation is to use seed-sowing experiments, but these do not enable the screening of large sets of species and habitats. In the present paper we present a complementary approach based on comparing small plots with larger regions with regard to species composition and distribution of functional traits. We developed a GIS tool based on ecological and geographical criteria to quantify species pools at various spatial scales. In this GIS tool, containing floristic, large databases, phytosociological and functional information are exploited. Our premise is that differences in the nature of the species in local and regional species pools with regard to functional traits can give important clues to the processes at work in the assembly of communities. We illustrate the approach with a case study for mesotrophic hay meadows (Calthion palustris). We tested the effects of differences in frequency in the local Habitat Species Pool and differences in dispersal and persistence traits of species on local species composition. Our results show that both species pool effects and functional traits affect the probability of occurrence in small plots. Species with a high propagule weight have, given the frequency in the Local Habitat Species Pool, a lower probability of occurrence in small plots. The probability of local occurrence, however, is increased by the ability to form a persistent soil seed bank and by adult longevity. This provides support for the view that the degree of dispersal limitation is dependent on the degree of spatial isolation of the focal site relative to source populations and moreover that species inherently differ in the degree to which dispersal limitation is a limiting factor for local occurrence.

Auditory apparent motion between sine waves differing in frequency.

The effects of frequency differences between the lead and lag stimuli on auditory apparent motion (AAM--the perception of continuous changes in the location of a sound image over time) were examined in two experiments. In experiment 1, three standard frequencies (500, 1000, and 5000 Hz) and three SOAs (40, 60, and 100 ms) were tested. Both standard frequency and stimulus onset asynchrony (SOA) were constant throughout a session. Eleven comparison frequencies were tested within each session, with the range dependent on the standard frequency. At standard frequencies of 500 and 1000 Hz, AAM was heard when the frequencies of the lead and lag stimuli were within 100 Hz of each other. At 5000 Hz, the range of frequencies producing AAM increased with SOA. In experiment 2, two standards (500 and 5000 Hz) were tested with a wider range of SOAs (10-210 ms) varied within a session, and a narrower range of comparison frequencies. Here, comparison frequency was constant throughout a session. At 500 Hz, the SOAs producing AAM did not depend on comparison frequency. At 5000 Hz, the SOAs producing AAM increased with comparison frequency, consistent with Korte's third law of visual apparent motion.

Frequency effects on cyclic plastic strain of polycrystalline copper under variable loading

Studies of material frequency effects in cumulative damage are rare. Since new work has shown that the frequency of cycling affects persistent slip band (PSB) formation, with large effects on cyclic plastic strain in load control tests, step-descending tests have been performed at various frequencies. The results show that in regimes of stress-strain where loop patches and PSBs are the prevailing structures, cyclic deformation following a load-descending step is significantly affected by frequency. For example, a frequency of 0.5 Hz at the low level can increase the current plastic strain in the specimen by as much as nearly two times over the same step test performed at 8 Hz. If the prevailing structure from which the step test is initiated consists of cell structure, the effect of frequency differences is found to be small. These results, interpreted in terms of structural changes and secondary dislocation behavior, show that frequency effects could be significant in the accumulation of fatigue damage, especially in variable loading.

Effect of frequency differences between blades of small radially axial turbines on their state of stress

The problem of the interaction of blades with slight frequency differences arouses considerable interest because of the influence which this interaction has on the scatter of stresses and on the stability of blading rings of gas turbines and axial compressors. Several authors showed [1-4] that frequency differences between interacting blades in resonance vibrations of blading rings considerably increase the amplitude of individual blades above the mean level. On the other hand, it was discovered [5, 6] that deliberately arranged difference in blade frequencies, attained by selective assembly, may yield a favorable effect in the attempt to control the free vibrations of compressor blades, and it may thus broaden the range of their stability. However, some aspects of the problem at hand require further investigation. For instance, in the above-mentioned works, the calculation models do not take into account the inertia coupling of the blades, yet under conditions of cophase excitation this leads to fundamentally new results. In [7], inertia coupling is taken into account but the case of cophase excitation is not being examined, and just there the existence of this kind of coupling is most important. Insufficient attention was also given to the influence of the scatter of damping properties of blades on their interaction. In this respect the results obtained in the present work differ considerably from the results presented in [i~ 2]. This is possibly due to the peculiarities of the object being investigated: the comparatively small relative mass of the rotor disk of a turbocompressor and the large scatter of the vibration decrements of individual blades.

Functional differences between rat islets of ventral and dorsal pancreatic origin.

Do functional linkages between islet endocrine cells exist? The effect of differences in frequency and distribution of islet endocrine cells on B cell function was examined in islets from the ventral (ventral islets) and dorsal (dorsal islets) areas of the rat pancreas. Dorsal islets contained 10 times as much glucagon as ventral islets, whereas insulin and total protein contents were similar. Basal rates of insulin secretion and proinsulin biosynthesis were similar in the two types of islet, but, under conditions of glucose stimulation, both insulin secretion and proinsulin biosynthesis were significantly greater in the glucagon-rich dorsal islets. Similarly, glucose utilization rates an ATP levels were greater in dorsal islets. In contrast, the rates of processing of newly synthesized proinsulin were similar in ventral and dorsal islets. That the islet glucagon content may have affected B cell function is inferred from two independent findings. Firstly, basal and glucose-stimulated cyclic AMP contents of glucagon-rich dorsal islets were greater than those of ventral islets. Secondly, in the presence of excess exogenous glucagon (1 microgram/ml), the differences in glucose-induced insulin secretion and proinsulin biosynthesis rates between the two types of islets were eliminated. These results strongly suggest that changes in the relative proportions of the different islet endocrine cells exert marked effects on islet function. In particular, a greater A cell and glucagon content is associated with higher rates of glucose-induced insulin secretion and biosynthesis.

Synchronisation of a p.c.m. network using digital techniques

In a network of interconnected digital p.c.m. telephone exchanges, all the signals should be virtually in synchronism to facilitate interconnections between channels on different routes. However, to maintain the security of the system, it is also desirable for each station to have an independent master oscillator. There are several possible methods for effectively synchronising the signals in such a system. Apart from the effect of frequency differences, synchronism is also affected by changes in the propagation delays of the interconnecting junctions, caused by temperature variations. A system is described in which the phase of an incoming signal is allowed to drift in relation to the signal generated locally, until a given limit is reached. The limit may conveniently be related to the amount of storage provided for temperature compensation of the junction delay. When the limit is reached, a digit is either added to, or omitted from, one of the signals during a part of the signal not carrying intelligence, such as a frame-synchronising period, so as to reduce the degree of asynchronism. This system adds some complexity to both the exchange master timing circuits and the received-signal timing circuits, and also complicates the switching of calls through the exchange. The time relationships between the various signals in the network can be deduced mathematically, allowing the behaviour of a network with a given set of initial conditions to be computed. Paralysis of the system can be avoided by a proper choice of the amount of storage.

Judgments of therelative frequency of sequential binary events: effects of frequency differences.

Judgments of therelative frequency of sequential binary events: effects of frequency differences.