A New Methodology for the Block Maxima Approach in Selecting the Optimal Block Size

The Block Maxima method divides sample data into equal blocks. Predictions are based on the maximum values of the observations. Choosing an efficient and proper block size for the Block Maxima method is an important issue and varies across fields (e.g., flood, rainfall, finance). However, the main problem is deciding which block size is suitable or optimal for the prediction. In the literature, it is a known fact that the selection of a small block size leads to bias, while the selection of a large block size leads to a variance problem. In one respect, this issue is any trade off problem between the bias and the variance. This paper proposes simple and easy computational method to specify the optimal block size selection process for the Block Maxima method

A time-symmetric individual block time step algorithm in n-body integration

Ayrık blok zaman adımlı integrasyon algoritmaları, çok-cisim problemlerinde sıklıkla kullanılan algoritmalardandır. Farklı zaman ölçeklerine sahip cisimlerin aynı problemin parçaları olduğu durumlarda, kullanımları kaçınılmazdır. Ancak kullanılan integrasyon şeması zaman-simetrik bile olsa, blok zaman adımları kullanıldığında zaman simetrisi bozulmaktadır. Zaman simetrisinin bozulmasının doğal sonucu, toplam enerji üzerindeki hata birikiminin doğrusal olarak artmasıdır. Bu çalışmada, zaman-simetrik blok zaman adımlı bir algoritma geliştirilmiştir. Geliştirilen algoritma, sabit zaman adımları kullanıldığında zaman-simetrik yapısını koruyan integrasyon şemalarının, değişken ayrık blok adımlı bir algoritma içerisinde de zaman simetrik yapısını korumasını sağlamaktadır. Hatta integrasyon şeması tam olarak zaman simetrik olmasa bile, geliştirilen algoritma ile yüksek enerji korunumu sağlandığı gözlenmiştir. Özellikle uzun süreli integrasyonlarda algoritmanın yüksek başarımı belirgindir. Zaman-simetrik ayrık blok zaman adımlı algoritma, bir yineleme yapısı içermektedir. Bu yinelemenin ayrık zaman adımlı integrasyon şemasıyla uygulanabilmesi için, çağ aralıkları (era) belirlenmiş, yineleme işlemleri bu çağ aralıkları üzerinden sağlanmıştır. Yapılan testlerde bu çağ aralıklarının büyüklüğünün hem yineleme sayısı, hem de bellek tüketimi açısından önemli olduğu gözlenmiştir. Çalışmanın bu safhasında, algoritma çağ aralıklarının değişken tutulabildiği bir yapıya kavuşturulmuştur. Algoritma Leapfrog integrasyon şeması kullanılarak geliştirilmiş, etkinliği daha yüksek dereceden integrasyon şemalarıyla da sınanmıştır. İçerdiği yineleme yapısı yüzünden ayrık zaman adımlı önceki algoritmalardan daha yüksek zaman ve bellek tüketimine sahiptir. Ancak toplam enerji üzerindeki hata birikimlerini büyük ölçüde azaltmaktadır. Anahtar Kelimeler: Çok-cisim problemi, sayısal integrasyon, ayrık blok-zaman adımları.The gravitational N-body problem can not be solved analytically except for two-body cases. While there are various approximate methods, such as Monte Carlo or Fokker-Planck method, the most accurate way to solve the N-body problem is by direct integration of the orbits of the N bodies. Direct integration of the N-body problem is a necessity for many cases such as star cluster simulations. During the last fifteen years, two approaches have been put forward to improve numerical conservation of energy and other theoretically conserved quantities: symplectic integration schemes, where the simulated system is guaranteed to follow a slightly perturbed Hamiltonian system, and time-symmetric integration schemes, where the simulated system follows the same trajectory in phase space, when run backward or forward. Time-symmetric integration schemes share with symplectic schemes the property that their energy errors show a much better behavior than the case for generic integration schemes. Allowing adaptive time steps typically leads to a loss of symplecticity. In contrast, time symmetry can be easily maintained, at least for a continuous choice of time step size. An iterative scheme must be combined with individual block time step scheme to apply the new algorithm to the n-body problem effectively. However, straightforward implementation of time-symmetry, translated to block time steps, faces significant hurdles for N-body problem. For example, iteration can lead to oscillatory behavior, and even when such behavior is suppressed, energy errors show a linear drift in time. In this work it is aimed to construct a time symmetric block time step integration scheme. We first consider to analyze block time step scheme with time symmetrization procedure for the gravitational two-body problem. It is hard to generate an efficient algorithm for N -body problem without deep and clear understanding of this fundamental problem. However it is easy to correct the algorithm in Kepler problem. Besides, it is known that contributions to the energy error are largely generated by close encounters between two particles. For these reasons, two-body problem is preferred to develop the algorithm in the first instance. The algorithm is developed and tested in two-body problem for accuracy and energy conservations in many different Kepler problem with different iteration numbers. In the process of the development work, leapfrog integration scheme which is the second order time-symmetry scheme is preferred. Also fourth, sixth, and eighth order Hermite integration schemes are used for test runs. The major conceptual difficulty in designing a time-symmetric block time step scheme is the global context information that is needed, with extensions toward the future as well as the past. We present an approach that circumvents these problems. We divide and conquer: we split the total history of our simulation into a number of smaller periods, which we call every one as era. Each era extends a period in time equal to the largest allowed time step tmax, or to an integer multiple of tmax, whatever turns out to be the most convenient. For such reasons, we have analyzed the era concept in more detail for time symmetrized block time steps. Our test results show that size of era must be chosen carefully for stable and robust integrations. This is important especially for long term simulations with highly desirable energy conservations. Era size is also important to avoid extra data storage and uselessly high number of iterations which require too much running times. As a second gain of the work, we re-designed the previous scheme, and suggested dynamically changing size for era. With this scheme, iteration process of the integration can follow needs of the simulation adaptively. And, era size will be well-adjusted with physics of the problem with proper criterion. Our basic integrator in the work is leapfrog scheme. It is a well known, second order, time symmetric integration scheme for fixed time steps. We also used fourth, sixth, and eighth order Hermite schemes to see the ability of the algorithm with higher order integration methods. We used different Kepler problems in two-body tests, and used Plummer model initial conditions for N-body tests. The algorithm does not show linear growing error with time symmetric integrations. It also shows high energy conservations with other integration schemes especially for long integration times. Keywords: N-Body integration, time symmetry, individual block - time step, Hermite integration

Physicochemical transformation of ZnO and TiO2 nanoparticles in sea water and its impact on bacterial toxicity

Background: The enormous properties of metal oxide nanoparticles make it possible to use these nanoparticles in a wide range of products. As their usage and application continue to expand, environmental health concerns have been raised. In order to understand the behavior and effect of metal oxide nanoparticles in the environment, comprehensive and comparable physicochemical and toxicological data on the environmental matrix are required. However, the behavior and effect of nanoparticles in the real environmental matrix, e.g. sea water, are still unknown. Methods: In this study, the effects of zinc oxide (ZnO) and titanium dioxide (TiO2) nanoparticles on the bacteria (gram positive-Bacillus subtilis, Staphylococcus aureus/gram-negative Escherichia coli, and Pseudomonas aeruginosa) in sea water were investigated. Furthermore, to better understand the behavior of the toxicity, surface chemistry, sedimentation, dissolution, particle size, and zeta potential of the nanoparticles dispersed in the sea water matrices were investigated using Fourier-transform infrared spectrometry (FTIR), ultraviolet–visible (UV-VIS) spectrophotometry, graphite furnace atomic absorption spectrometer (GFAAS), and dynamic light scattering (DLS), respectively. Results: The environmental matrix had a significant influence on physicochemical behavior of the tested nanoparticles. Besides, the inhibition of tested bacteria was observed against ZnO and TiO2 nanoparticles in the presence of sea water, while there was no inhibition in the controlled condition. Conclusion: The results demonstrate that surface chemistry with exposure to the sea water can have a significant role on the physicochemical properties of nanoparticles and their toxicity. Keywords: Nanoparticle toxicity, Titanium dioxide, Zinc oxide, Sea water, Physicochemical properties, Matrix effec

Volume CXIV, Number 4, November 7, 1996

Objective: Turner syndrome (TS) is a chromosomal disorder caused by complete or partial X chromosome monosomy that manifests various clinical features depending on the karyotype and on the genetic background of affected girls. This study aimed to systematically investigate the key clinical features of TS in relationship to karyotype in a large pediatric Turkish patient population.Methods: Our retrospective study included 842 karyotype-proven TS patients aged 0-18 years who were evaluated in 35 different centers in Turkey in the years 2013-2014.Results: The most common karyotype was 45,X (50.7%), followed by 45,X/46,XX (10.8%), 46,X,i(Xq) (10.1%) and 45,X/46,X,i(Xq) (9.5%). Mean age at diagnosis was 10.2±4.4 years. The most common presenting complaints were short stature and delayed puberty. Among patients diagnosed before age one year, the ratio of karyotype 45,X was significantly higher than that of other karyotype groups. Cardiac defects (bicuspid aortic valve, coarctation of the aorta and aortic stenosis) were the most common congenital anomalies, occurring in 25% of the TS cases. This was followed by urinary system anomalies (horseshoe kidney, double collector duct system and renal rotation) detected in 16.3%. Hashimoto's thyroiditis was found in 11.1% of patients, gastrointestinal abnormalities in 8.9%, ear nose and throat problems in 22.6%, dermatologic problems in 21.8% and osteoporosis in 15.3%. Learning difficulties and/or psychosocial problems were encountered in 39.1%. Insulin resistance and impaired fasting glucose were detected in 3.4% and 2.2%, respectively. Dyslipidemia prevalence was 11.4%.Conclusion: This comprehensive study systematically evaluated the largest group of karyotype-proven TS girls to date. The karyotype distribution, congenital anomaly and comorbidity profile closely parallel that from other countries and support the need for close medical surveillance of these complex patients throughout their lifespa

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

<em>Quantum Degeneracy Effect on the Work Output from A Stirling Cycle</em>

The effect of quantum degeneracy on the work output from a Stirling cycle working at quantum degeneracy conditions (QDCs) is analyzed. Expressions for net work outputs of Stirling power cycles working with monatomic ideal Bose and Fermi gases are derived by using the quantum ideal gas equation of state. Ratios of net work outputs of Stirling cycles working with Bose and Fermi gases to the net work output of a classical Stirling cycle (RBW and RWF, respectively) are obtained. Variations of RBW and RFW with TH are examined for a given temperature ratio (τ=TL/TH) and a specific volume ratio (rν=νH/νL). At QDC, it is seen that RBW has a maximum value, which is greater than unity. On the other hand, there is no maximum or minimum point for RFW and RFW⩽1 for any values of TH. Consequently, the use of Bose gas as a working fluid in a Stirling cycle provides an advantage since it causes the net work output per cycle to increase by consuming more heat energy. This fact is seen to be in the opposite direction for a Stirling cycle working with Fermi gas.</p