Sampling hidden populations is challenging due to the lack of convenience statistical frames. Since most populations exposed to special diseases are hidden and hard to reach, Sampling methods that produce representative and efficient samples from the populations have become a study subject for researches all over the world. Because of the unknown probability of selecting samples in conventional Sampling methods and also invalidity of generalizing the results of non-probability Sampling methods to the statistical population, the necessity of introducing probability chain-referral Sampling methods, such as the respondent driven Sampling method becomes imperative. In this article, besides introducing the respondent driven Sampling method, some of the advantages of this method as relative decrease of the bias of estimates, declining the non-response rate by paying incentives and allocating weights proportional to reciprocal of the social network size of respondents to produce unbiased estimates are described. Moreover, some disadvantages of this method such as lack of producing differential samples by selecting similar seeds, lack of reaching more efficient method than snowball Sampling by implementing this method improperly and lack of achieving to equilibrium by existing weak social networks among members of interested population are stated. Another aim of this article is to compare Sampling methods of hidden population with the respondent driven Sampling method which are the results of implementing this method in different surveys and existing simulations.

On the use of Sampling and qualitative case study approach, Brickhouse explored three science teachers' insights into the relationship between science and technology and the impact of such insights on classroom practice, and in 1990 tested a similar teacher relationship between understanding the nature of science and classroom practice. During the four months, a minimum of four hours of interviews and thirty-five hours of class observations (taped) were collected for each teacher. Additional data was also collected through tests, classroom exams, and training materials. Additional data was also collected through tests, classroom exams, and training materials. Two teachers, who were also experienced teachers, showed classroom exercises that were in line with their own vision and philosophy, while at first the classroom exercises were not in line with their beliefs. Institutional (formal) constraints have been expressed as barriers to translating teachers' beliefs into education.

The exact manner of BKZ algorithm for higher block sizes cannot be studied by practical running, so simulation of BKZ can be used to predict the total cost and output quality of BKZ algorithm. Sampling method of enumeration solution vector v is one of the main components of designing BKZ-simulation and can be divided into two phases: Sampling norm of solution vector v and Sampling corresponding coefficient vectors. This paper introduces a simple and efficient idea for Sampling the norm of enumeration solution v for any success probability of enumeration bounding functions, while to the best of our knowledge, no such Sampling method for norm of enumeration solution is proposed in former studies. Next, this paper analyzes the structure and probability distribution of coefficient vectors (corresponding with enumeration solution v), and consequently introduces the Sampling methods for these coefficient vectors which are verified by our test results, while no such a deep analysis for Sampling coefficient vectors is considered in design of former BKZ-simulations. Moreover, this paper proposes an approximation for cost of enumerations pruned by optimal bounding functions.

Background: Chorionic villus Sampling (CVS) has a major role in prenatal diagnosis. It is an invasive diagnostic method in completion of primary prenatal screenings. This article is a report of our 8 years experience of CVS in Mashhad.Materials and methods: We have done 1511 cases of invasive diagnostic procedure including 723 CVS which were included in our study and also 788 cases of amniocentesis. The gestational ages of the patients whom CVS were done for them were between 10 to 22 weeks based on the LMP. All CVS's were done by 19.5 G needles under Ultrasonographic real time guide using freehand method by a radiologist.Results: Mean gestational age at the time of procedure was 12.5 weeks. The most common cause of CVS application was due to beta thalassemia (81%) followed by karyotype (7%), spinal muscular atrophy (werding Hoffman syndrome) (3.3%), Congenital adrenal hyperplasia (2.7%), Duchene muscular dystrophy (3%), and hemophilia, achondroplasia, paternity test, cystinuria, PKU in remaining cases. Needle insertions into placenta were done for 1 time in 517 patients (71.5%), 2 times in 163 patients (22.5%), 3 times in 38 patients (5.2%) and 4 times in 5 patients (0.7%). Any gestational complications within 1 months of CVS were considered as the complication of our procedure.As the complication of the CVS there were 13 cases of spotting without miscarriage (1.8%) and 5 cases of miscarriage (0.7%) including 3 cases of fetal death (0.4%) and one case of abortion (0.1%).Conclusion: CVS is considered as an invasive diagnostic method in early pregnancies but it's benefits outweighing the complications in all cases that it is indicated.

In this paper, solution of inverse problems in a plane linear elastic bodies are investigated. In recent years, many studies have been conducted to develop effective approaches for damage detection in structural components. The efforts made over the last decades to overcome the mathematical challenges encountered in non-linear inverse problems may be categorized in two procedures: traditional methods, and qualitative methods. Although satisfactory results can be obtained using traditional approaches, they impose long reconstruction times associated with necessity of an accurate initial guess. These schemes require a priori information that may not be necessarily available. Consequently, the mentioned limitations have led to the conceptually distinct class of inverse scattering solutions, known as “, qualitative methods. ”,These methods are based on non-iterative obstacle reconstruction from far-and/or near-field measurements of the scattered field which avoids incorrect model assumption. Qualitative methods may be considered as probe/Sampling methods such as linear Sampling method, topological sensitivity, factorization method, and point source method, which seek to determine the geometric properties of scatterers. In this regard, the LSM and the FM introduced in the inverse scattering literature of far-field acoustics for the first time, are particularly attractive. This is due to the abilities of these methods to provide accurate reconstruction of the location and shape of the unknown scatterer from measurements of near-or far-field patterns, by monitoring the behavior of the norm of regularized solution. This norm is bounded inside the targets and unbounded elsewhere. Moreover, the most interesting feature of qualitative methods is that they do not require a priori information/assumption on the scatterer and/or the investigation domain. In addition, these methods may handle multiple scatterers as easily as single ones. Furthermore, these methods involve relatively low computational cost and can be applied to various types of defects such as non-convex and not-connected ones. For this purpose, Sampling method in frequency domain is introduced for cavity/crack detection in a structural element such as plate. This goal is followed by partitioning the investigated region into an arbitrary grid of Sampling points, in which a linear equation is solved. The main idea of the linear Sampling method is to search for a superposition of differential displacement fields which matches with a prescribed radiating solution of the homogeneous governing equation in Ω, (D), for each Sampling point. Although this method has been used in the context of inverse problems such as acoustics, and electromagnetism, there is no specific attempt to apply this method to identification of crack/cavities in a structural component. This study emphasizes the implementation of the Sampling method in the frequency domain using spectral finite element method. A set of numerical simulations on two-dimensional problems is presented to highlight many effective features of the proposed qualitative identification method.

Linear Sampling method (LSM) is a simple and effective method for the shape reconstruction of unknown objects. It is also a fast and robust method to find the location of an object. This method is based on far field operator which relates the far field radiation to its associated line source in the object. There has been an extensive research on different aspects of the method. But from the experimental point of view there has been little research especially on the effect of polarization on the imaging quality of the method. In this paper, we study the effect of polarization on the quality of shape reconstruction of two dimensional targets. Some examples are illustrated to compare the effect of transverse electric (TE) and transverse magnetic (TM) polarizations, on the reconstruction quality of penetrable and non-penetrable objects.

Joint-point method is one of the distance Sampling methods for forest inventory. For estimation of tree density with joint-point Sampling method two estimator suggested by Batcheler and also Engeman et al. that biased in nonrandom spatial pattern. Aim of this study was presentation a new unbiased and most efficiency estimator for this method. Forty-four sample size for each of six Sampling methods: Circle plot (10ar as true value), Nearest individual method, nearest neighbor method, Compound method, second nearest neighbor method and Joint-point method in forests of Sorkheh dizeh Dalahoo of Kermanshah province with systematic random design (100m*100m) carried out. After that trees density of forest stand calculated with 10 estimators of above methods and new estimator. Then calculated density with new estimator compared with Batcheler and Engeman et al. estimators and other estimators in different spatial patterns (regular, random and aggregate) by precision and accuracy criteria. The results showed that this new estimator was not only most efficient than Batcheler and Engeman et al. estimators but also was best than other estimators.

Precise quantitative information of the young forest stands is necessary in their scientific and technical management and direction of the forest stands toward sustainability. In plantations, the working unit can be a single tree rather than the area, or the smaller areas of Sampling can be used for measurement. N-tree Sampling method is one of the distance techniques used for measuring the quantitative and qualitative characteristics in forest stands. In this study N-tree Sampling methods (3, 4, 5, 6, 7, 8, 9 and 10) were assessed to measure number, basal area and volume per hectare in a 12-ha plantation in the north of Iran. At first the plantation was fully callipered. Then a 50×50 m grid was determined for N-tree Sampling method application. The result of t-test showed that mean in basal area per hectare estimated by Prodan's estimator, in 5, 6 and 7 trees had significant difference with 100% inventory, but means estimation of these characteristics from other methods was acceptable. Estimating means in the number per hectare and volume in hectare by Prodan's estimator did not have any significant difference with 100% inventory in the all of N-tree Sampling methods. At last, using E%2×T, the 4 tree distance Sampling method was suitable for Sampling in populos delteoides plantations.