Certain Number Of Times Research Articles

Stability of the singly resonant optical parametric oscillator

We show that plane-wave singly resonant optical parametric oscillators exhibit a temporal modulation instability when pumped a certain number of times above threshold. Previously, this instability threshold was predicted, with a model neglecting variations in pump power, to occur at around 4.61 times oscillation threshold. We consider here the full self-consistent interaction between pump, signal, and idler sidebands and find that in some spectral regions the instability threshold can be lower than previously predicted, in some cases even comparable to the oscillation threshold, preventing single mode operation at high conversion efficiency. We examine the behavior of the instability for typical regions of operation, and find that both group velocity mismatches and group velocity dispersion have a significant effect. The instability can be suppressed by a suitable choice of intracavity etalon, the design constraints of which are determined.

Verifying resource access control on mobile interactive devices

A model of resource access control is presented in which the access control to resources can employ user interaction to obtain the necessary permissions. This model is inspired by and improves on the Java security architecture used in Java-enabled mobile telephones. We extend the Java model to include access control permissions with multiplicities in order to allow to use a permission a certain number of times. We define a program model based on control flow graphs together with its operational semantics and provide a formal definition of the basic security policy to enforce viz that an application will always ask for a permission before using it to access a resource. A static analysis which enforces the security policy is defined and proved correct. A constraint solving algorithm implementing the analysis is presented.

Zahlbegriff und Zählverhalten bei Tieren. Neue Versuche und Deutungen

Pigeons were trained to peck a certain number of times at a target, the number of pecks being consistently different from the number of light spots previously shown to them. This proved as easy to achieve as the usual experimental combination of equal numbers, both perceived and performed. There is no reason to assume that animals have an abstract number conception in the human sense of the word. Nor is there evidence in animals for number transfer between perception and performance, or for spontaneous combination of successive and simultaneous presentation of quantities. Results obtained by earlier authors have been over-interpreted in the literature.

자동결함 검출시스템에서 결함크기 측정오차로 인한 오검률의 통계적 예측

AVI (Automatic Vision Inspection) systems automatically detect defect features and measure their sizes via camera vision. It is important to predict the performance of an AVI to meet customer's specification in advance. Also the prediction can indicate the level of current performance of an AVI system. In this paper, we propose a statistical method for prediction of false alarm rate regarding inconsistency of defect size measurement process. For this purpose, only simple experiments are needed to measure the defect sizes for certain number of times. The statistical features from the experiment are utilized in the prediction process. Therefore, the proposed method is swift and easy to implement and use. The experiment shows a close prediction compared to manual inspection results.

Structural properties of Euclidean rhythms

In this paper we investigate the structure of Euclidean rhythms and show that a Euclidean rhythm is formed of a pattern, called the main pattern, repeated a certain number of times, followed possibly by one extra pattern, the tail pattern. We thoroughly study the recursive nature of Euclidean rhythms when generated by Bjorklund's algorithm, one of the many algorithms that generate Euclidean rhythms. We make connections between Euclidean rhythms and Bezout's theorem. We also prove that the decomposition obtained is minimal.

A countable and time-bound password-based user authentication scheme for the applications of electronic commerce

In this paper, we propose a secure and efficient user authentication scheme with countable and time-bound features. The countable feature is to limit the use to a certain number of times, which means that the users are able to successfully log into the system in a fixed number of times. The feature of the time-bound allows each login ticket to have a period of expiration. In other words, if a login request is overdue, it would not be available anymore. These features make our scheme more reliable for applications in the field of electronic commerce, such as on-line games, pay-TV, and so on. Since our scheme does not require any password or verification table and can avoid replay attacks, it is under firm security. Moreover, our scheme shows a lower computational overhead on the user side. Therefore, it offers an efficient and adequate alternative for the implementations in the mobile environment with limited computing capability.

Editorial: Stem cell therapy: how should nurses respond?

Editorial: Stem cell therapy: how should nurses respond?

Studies of the collision frequency of ideal gas particles with the surfaces of the objects created using the ballistic deposition technique

This paper is a continuation of our studies of the collision frequency of ideal gas particles with the rough/fractal surfaces. Here, we applied a more realistic surface growth model, i.e. ballistic deposition for creation of fractal objects. We found that the collision frequency with irregular surfaces is the linear function of pressure and this frequency per unit pressure is quite a complicated function of the surface fractal dimension as well as the diameter of colliding particle. The collision frequency with rough surfaces cannot be exactly described by the analytical formula called the Langmuir–Hertz equation. However, we have stated that the deviations of the true collision frequency from the Langmuir–Hertz prediction are not huge and in typical catalytic studies the error introduced by replacing the true frequency by the Langmuir–Hertz prediction can be safely neglected. We have also studied the probability of finding on the surface an atom which has been hit a certain number of times by a gas particle. This probability reveals an interesting behaviour for small gas particles, i.e. it perfectly correlates with the number of directions from which the surface atom is accessible from the gas phase. We have also estimated the evolution of the adsorption energy distribution with the increasing fractal dimension of the surface in the ballistic deposition.

Effects of asymmetric dispersal and environmental gradients on the stability of host–parasitoid systems

We consider host–parasitoid systems spatially distributed on a row of patches connected by dispersal. We analyze the effects of dispersal frequency, dispersal asymmetry, number of patches and environmental gradients on the stability of the host–parasitoid interactions. To take into account dispersal frequency, the hosts and parasitoids are allowed to move from one patch to a neighboring patch a certain number of times within a generation. When this number is high, aggregation methods can be used to simplify the proposed initial model into an aggregated model describing the dynamics of both the total host and parasitoid populations. We show that as the number of patches increases less asymmetric parasitoid dispersal rates are required for stability. We found that the ‘CV2>1 rule’ is a valid approximation for stability if host growth rate is low, otherwise the general condition of stability we establish should be preferred. Environmental variability along the row of patches is introduced as gradients on host growth rate and parasitoid searching efficiency. We show that stability is more likely when parasitoids move preferentially towards patches where they have high searching efficiency or when hosts go mainly to patches where they have a low growth rate.

Risk Neutral Probabilities and Option Bounds: A Geometric Approach

In this paper we first present a geometric approach to option bounds. We show that if two risk neutral probability density functions intersect for certain number of times, then comparing the fatness of their tails we can tell which of them gives higher option prices. Thus we can derive option bounds by identifying the risk neutral probability density function which intersects all admissible ones for certain number of times. Applying this approach we tighten the first order stochastic dominance option bounds from concurrently expiring options when the maximum value of the risk neutral density are known.

Approval of Virtual Reality Training for Carotid Stenting

PERCUTANEOUS ENDOVASCULAR PROCEDURES CONFER benefits to patients similar to those seen with minimally invasive surgery, such as minimal invasion of the body cavity, reduced pain, shortened recovery time, and more rapid return to work. However, minimally invasive surgery and endovascular procedures also share similar problems. As with minimally invasive surgery, endovascular procedures require physicians to perform invasive procedures guided by 2-dimensional video images while using and manipulating tools with limited degrees of freedom. Endovascular procedures also require the operator to adapt to significantly decreased tactile sensation and overcome similar proprioceptive-visual conflict issues from manipulating long wires or instruments that can fulcrum against the body wall. These hurdles combine to create substantial challenges for physicians training to acquire these skills. The challenge of training physicians for performance of endovascular procedures has been brought to the forefront because of the rapidly expanding application of carotid stenting for treatment of carotid artery stenosis into the broader medical marketplace. Currently, few physicians are experienced in the carotid stenting technique. However, with the recent US Food and Drug Administration (FDA) approval of cartoid stents, many physicians from multiple specialties will want to learn the carotid stenting technique. Traditional training methods for new procedures include performing the procedure on animals, cadavers, or mechanical models or supervised performance of the procedure on patients. Inherent problems with these traditional training strategies include the ethical and anatomical problems of training on animals, risks posed with repeated exposure to radiation, and the expense of consuming real medical devices. However, the majority of procedural training in the United States still occurs on patients with direct mentoring by experienced physicians during an actual clinical procedure. This tradition of training on patients has raised concern among the profession and the public about how physicians will acquire sufficient skill to safely perform new, potentially high-risk, endovascular procedures such as carotid stenting. Because the carotid arteries are the primary blood vessels to the brain, if an embolus of thrombotic plaque dislodges and enters the brain during a carotid stent procedure, the patient could have a stroke or die on the operating table. As with other procedures, carotid stenting has a definite learning curve. However, unlike many other procedures, the risk conferred to the patient in this procedure from the physicians’ learning curve is unacceptably high. Traditionally, it was assumed that if a physician performed a procedure a certain number of times or trained for a period of time then that physician became proficient in the procedure. However, essentially no mechanism for measuring posttraining skill has been used. Both number of procedures and duration of training are, at best, crude surrogate measures of skill and fail to factor in the variability in individual rates of learning. This approach to training produces physicians with considerably variable skills that have been only subjectively assessed by those who trained them. This variation is particularly important with carotid stenting because this procedure crosses multiple clinical specialties with each bringing a different skill set to the training table. For example, a vascular surgeon has a thorough cognitive understanding of vascular anatomy and management of carotid disease but may lack some of the psychomotor technical skills of wire and catheter manipulation and may be unfamiliar with management of the fluoroscope. Conversely, an interventional cardiologist will have the technical skill with catheter-based

ON THE RECOVERY OF A CURVE ISOMETRICALLY IMMERSED IN

It is known from classical differential geometry that one can reconstruct a curve with (n-1) prescribed curvature functions, if these functions can be differentiated a certain number of times in the usual sense and if the first (n-2) functions are strictly positive. It is established here that this result still holds under the assumption that the curvature functions belong to some Sobolev spaces, by using the notion of derivative in the distributional sense. It is also shown that the mapping which associates with such prescribed curvature functions the reconstructed curve is of class ${\mathcal C}^\infty$.

On the recovery of a curve isometrically immersed in a Euclidean space

It is known from differential geometry that one can reconstruct a curve with n−1 prescribed curvature functions, if these functions can be differentiated a certain number of times in the usual sense and if the first n−2 functions are strictly positive. We establish here that this result still holds under the assumption that the curvature functions belong to some Sobolev spaces, by using the notion of derivative in the distributional sense. We also show that the mapping that associates with such prescribed curvature functions the reconstructed curve is of class C ∞ . To cite this article: M. Szopos, C. R. Acad. Sci. Paris, Ser. I 338 (2004).

Statistical models for protein validation using tandem mass spectral data and protein amino acid sequence databases.

The purpose of this work is to develop and verify statistical models for protein identification using peptide identifications derived from the results of tandem mass spectral database searches. Recently we have presented a probabilistic model for peptide identification that uses hypergeometric distribution to approximate fragment ion matches of database peptide sequences to experimental tandem mass spectra. Here we apply statistical models to the database search results to validate protein identifications. For this we formulate the protein identification problem in terms of two independent models, two-hypothesis binomial and multinomial models, which use the hypergeometric probabilities and cross-correlation scores, respectively. Each database search result is assumed to be a probabilistic event. The Bernoulli event has two outcomes: a protein is either identified or not. The probability of identifying a protein at each Bernoulli event is determined from relative length of the protein in the database (the null hypothesis) or the hypergeometric probability scores of the protein's peptides (the alternative hypothesis). We then calculate the binomial probability that the protein will be observed a certain number of times (number of database matches to its peptides) given the size of the data set (number of spectra) and the probability of protein identification at each Bernoulli event. The ratio of the probabilities from these two hypotheses (maximum likelihood ratio) is used as a test statistic to discriminate between true and false identifications. The significance and confidence levels of protein identifications are calculated from the model distributions. The multinomial model combines the database search results and generates an observed frequency distribution of cross-correlation scores (grouped into bins) between experimental spectra and identified amino acid sequences. The frequency distribution is used to generate p-value probabilities of each score bin. The probabilities are then normalized with respect to score bins to generate normalized probabilities of all score bins. A protein identification probability is the multinomial probability of observing the given set of peptide scores. To reduce the effect of random matches, we employ a marginalized multinomial model for small values of cross-correlation scores. We demonstrate that the combination of the two independent methods provides a useful tool for protein identification from results of database search using tandem mass spectra. A receiver operating characteristic curve demonstrates the sensitivity and accuracy level of the approach. The shortcomings of the models are related to the cases when protein assignment is based on unusual peptide fragmentation patterns that dominate over the model encoded in the peptide identification process. We have implemented the approach in a program called PROT_PROBE.

Migration Frequency and the Persistence of Host-Parasitoid Interactions

This paper analyses the effect of migration frequency on the stability and persistence of a host–-parasitoid system in a two-patch environment. The hosts and parasitoids are allowed to move from one patch to the other a certain number of times within a generation. When this number is low, i.e. when the time-scales associated with migration and demography are of the same order, host–-parasitoid interactions are usually not persistent. When this number is high, however, persistence is more likely. Moreover, in this situation, aggregation methods can be used to simplify the proposed initial model into an aggregated model describing the dynamics of both the total host and parasitoid populations. Analysis of the aggregated model shows that the system reaches a stable steady state for some regions of the parameter domain. Persistence occurs when the movement of the parasitoids is asymmetrical, i.e. they move preferentially to one of the two patches. We show that the growth rate of the host population is a key parameter in determining which migration strategies of the parasitoids lead to persistent host–-parasitoid interactions.

Migration Frequency and the Persistence of Host-Parasitoid Interactions

This paper analyses the effect of migration frequency on the stability and persistence of a host–-parasitoid system in a two-patch environment. The hosts and parasitoids are allowed to move from one patch to the other a certain number of times within a generation. When this number is low, i.e. when the time-scales associated with migration and demography are of the same order, host–-parasitoid interactions are usually not persistent. When this number is high, however, persistence is more likely. Moreover, in this situation, aggregation methods can be used to simplify the proposed initial model into an aggregated model describing the dynamics of both the total host and parasitoid populations. Analysis of the aggregated model shows that the system reaches a stable steady state for some regions of the parameter domain. Persistence occurs when the movement of the parasitoids is asymmetrical, i.e. they move preferentially to one of the two patches. We show that the growth rate of the host population is a key parameter in determining which migration strategies of the parasitoids lead to persistent host–-parasitoid interactions.

Testing trends in environmental compliance

Many environmentalregulations are based on threshold levels. Such a level is generally set such that exposure to a toxin above the level is considered a hazard to health. In many instances, the level may be exceeded a certain number of times before regulatory action is taken. Such is the case with the National Ambient Air Quality Standards (NAAQS) set by the Environmental Protection Agency (EPA) in accordance with the 1990 amendment of the Clean Air Act of 1970. This set of standards sets threshold levels for several pollutants including carbon monoxide, nitrogen dioxide, ground-level ozone, and lead. Many areas of the United States, which the EPA designates as nonattainment areas, persistently exceed the air pollution levels set by the NAAQS. Progress in these areas is of ten slow but can be studied through data collected on the elapsed time between violations. The purpose of this article is to present a relatively easy but flexible statistical method for assessing whether an area is making progress with compliance to the NAAQS. The method presented in this article is based on a randomization test of a general model for the mean time between violations of the standard. The modeling-type approach of this method makes it flexible enough to study many types of trends. The use of the randomization test makes the method simple to apply and requires fewer assumptions than many other proposed methods. We discuss some general theoretical conditions for which the method is well suited and study the performance of this method empirically, Finally, we apply the method to a well-known set of interviolation times corresponding to data collected on ground-level ozone in Houston, Texas.

Analysis of third-party warehousing contracts with commitments

This paper considers multi-period warehousing contracts under random space demand. A typical contract is specified by a starting space commitment plus a certain number of times at which the commitment can be further modified. Three forms of contracts are analysed: (1) there is a restriction on the range of commitment changes and the schedule for the changes is preset by the warehouser; (2) the same as form (1) but there is no restriction on the range; (3) the same as form (2) but the schedule for the changes is chosen by the user. We explore properties and algorithms for the three problems from the user's perspective. Solutions of simple form are obtained for the first two models and an efficient dynamic programming (DP) procedure is proposed for the last. A numerical comparison of the total expected leasing costs suggests that under certain demand patterns, contract forms (2) and (3) could be cost effective.

Defaults and interest rates in international lending

Since lenders cannot observe the riskiness of the projects that borrowers could choose, interest rates alone cannot be used as an instrument to discipline borrowers. A credible threat to exclude borrowers who default more than a certain number of times from participating in the capital markets makes international debt contracts incentive compatible. Since larger borrowers get fewer chances to default, they choose safer projects and are therefore charged lower interest rates. Also, borrowers, after each successive default, switch to safer and safer projects, which may result in lower and lower interest rates. This paper provides empirical evidence supporting these two predictions.

Matching of numerical symbols with number of responses by pigeons

Pigeons were trained to peck a certain number of times on a key that displayed one of several possible numerical symbols. The particular symbol displayed indicated the number of times that the key had to be pecked. The pigeons signalled the completion of the requirement by operating a separate key. They received a food reward for correct response sequences and time-out penalties for incorrect response sequences. In the first experiment nine pigeons learned to allocate 1, 2, 3 or 4 pecks to the corresponding numerosity symbols s 1, s 2, s 3 and s 4 with levels of accuracy well above chance. The second experiment explored the maximum set of numerosities that the pigeons were capable of handling concurrently. Six of the pigeons coped with an s 1–s 5 task and four pigeons even managed an s 1–s 6 task with performances that were significantly above chance. Analysis of response times suggested that the pigeons were mainly relying on a number-based rather than on a time-based strategy.