Variational Boundary Conditions for Molecular Dynamics Simulations of Solids at Low Temperature

Boundary conditions for molecular dynamics simulation of crystalline solids are considered with the objective of eliminating the reflection of phonons. A variational formalism is presented to construct boundary conditions that minimize total phonon reflection. Local boundary conditions that involve a few neighbors of the boundary atoms and limited number of time steps are found using the variational formalism. Their effects are studied and compared with other boundary conditions such as truncated exact boundary conditions or by appending border atoms where artificial damping forces are applied. In general it is found that, with the same cost or complexity, the variational boundary conditions perform much better than the truncated exact boundary conditions or by appending border atoms with empirical damping profiles. Practical issues of implementation are discussed for real crystals. Application to brittle fracture dynamics is illustrated.     

Benign surgical diseases of the gastro-oesophageal junction

Benign surgical conditions of the oesophago-gastric junction (OGJ) are important causes of morbidity and in some cases mortality for patients. This chapter discusses both elective and emergency benign disorders of the OGJ, their investigation and management. Elective conditions include gastro-oesophageal reflux disease (GORD), giant para-oesophageal hiatal herniae (GPHH), achalasia and other motility disorders. These conditions are now usually all managed laparoscopically when operative intervention is required. Emergency conditions include acute presentations of giant para-oesophageal hiatal herniae and OGJ perforations including Boerhaave's syndrome. These conditions present diagnostic and management challenges to the surgeon and are associated with significant morbidity and mortality. Varices, gastro-intestinal stromal tumours (GISTs), ulcers and bleeding are not discussed in this article.     

Classification of musculoskeletal spinal conditions*

The aim of this article is to present and discuss the classification of musculoskeletal spinal conditions. The major classifications presented are muscle, joint, and nerve root. Many different conditions are presented under each of these major classifications with emphasis on those conditions commonly seen in a physical therapy clinic. The clinical picture of each condition is presented showing the significant findings in the history, structural, mobility, neurological, and palpation exams. Treatment suggestions are presented to help clarify the differences between conditions, and to stress the importance of evaluation and classification before planning treatment. The author also stresses the interrelationship and progressive nature of certain conditions.J Orthop Sports Phys Ther 1979;1(1):3-15.     

High-order necessary optimality conditions for control problems with terminal constraints

This is a survey of high-order necessary optimality conditions for control problems with inequality and equality terminal constraints. Both classical and Pontryagin extremals are considered. For classical extremals, the characteristics of necessary optimality conditions in terms of variations are given, and the investigations devoted to Kelley's conditions are discussed in detail. For Pontryagin extremals, two types of results are given: generalizations and extensions of matrix impulse optimality condition and high-order maximum principle.     

Arthritis and related diseases of the foot and ankle: rehabilitation and biomechanical considerations

Arthritis and other rheumatic conditions are among the most common disabilities in the United States. Although arthritic conditions affect the knee and hip joints more frequently than the joints of the foot, disorders of the foot are particularly disabling. This article outlines the types of arthritis conditions affecting the foot and discusses strategies for management and rehabilitation.     

The changing face of disability in the US Army: the Operation Enduring Freedom and Operation Iraqi Freedom effect

Orthopaedic disorders account for significant disability among adults in the United States. Previous studies have demonstrated long-term disability in military personnel with musculoskeletal conditions. However, these studies focused primarily on battlefield-injured service members and did not evaluate the entire population. The goal of this study was to determine and compare the disabling conditions of the entire United States Army during peacetime and war. We identified the conditions leading to separation from military service before and during Operation Iraqi Freedom and Operation Enduring Freedom. During war, more soldiers are found to be unfit for duty, and they have more conditions per individual that make them unfit. Orthopaedic conditions account for the greatest number of soldiers separated from military service at both time points studied (ie, January through March 2001, January through March 2009). Back pain and osteoarthritis are the two most common causes of separation from military service; these conditions are responsible for the most disability during peacetime and war.     

Benign surgical diseases of the gastro-oesophageal junction

Benign surgical conditions of the oesophagogastric junction (OGJ) are important causes of morbidity and in some cases mortality for patients. This article discusses both elective and emergency benign disorders of the OGJ, including their investigation and management. Elective conditions include gastro-oesophageal reflux disease (GORD), giant para-oesophageal hiatal herniae (GPHH), achalasia and other motility disorders. These conditions are now usually all managed laparoscopically when operative intervention is required. Emergency conditions include acute presentations of giant para-oesophageal hiatal herniae and OGJ perforations including Boerhaave's syndrome. These present diagnostic and management challenges to the surgeon and are associated with significant morbidity and mortality. Varices, gastro-intestinal stromal tumours (GISTS), ulcers and bleeding are not discussed in this article.     

Genetic susceptibility to skin cancers

Hereditary syndromes of predisposition to skin cancer are rare conditions with several different modes of transmission (autosomal recessive, dominant or X-linked). These conditions predispose principally to skin tumors, but sometimes, although more rarely, to some visceral tumors. The clinical and histologic characteristics of the tumors observed in these conditions are generally identical to those of sporadic forms. They are distinguished, however, by their multiple number and their earlier onset.     

Intratubular crystallization events

Can urolithiasis start as an intratubular event? Under severe hyperoxaluric conditions in animal models at least crystal formation can. Recently models have been presented that assess the chances of crystal formation under more normal conditions. These models describe changes in fluid composition as this passes through the nephron, these conditions being simulated in in vitro experiments. It appears that under naturally occurring intratubular conditions calcium-salt crystallization takes place within the time tubular fluid normally spends in the nephron. Precipitation starts with a calcium-phosphate phase under conditions found in the thin limbs. This crystalline phase then (partly) dissolves when collecting duct conditions are used, thereby inducing formation of calcium oxalates. Under these conditions the latter increase in size by way of crystal growth and agglomeration. Large particle formation and cell adhesion can eventually result in particle retention and subsequent stone formation. Viewing urolithiasis as originally an intratubular event has consequences for in vitro experiments and treatments, which are discussed in this paper.     

LQ‐optimal control of positive linear systems

The LQ₊ problem, i.e. the finite‐horizon linear quadratic optimal control problem with nonnegative state constraints, is studied for positive linear systems in continuous time and in discrete time. Necessary and sufficient optimality conditions are obtained by using the maximum principle. These conditions lead to a computational method for the solution of the LQ₊ problem by means of a corresponding Hamiltonian system. In addition, the necessary and sufficient conditions are proved for the LQ₊‐optimal control to be given by the standard LQ‐optimal state feedback law. Then sufficient conditions are established for the positivity of the LQ‐optimal closed‐loop system. In particular, such conditions are obtained for the problem of minimal energy control with penalization of the final state. Moreover, a positivity criterion for the LQ‐optimal closed‐loop system is derived for positive discrete‐time systems with a positively invertible (dynamics) generator. The main results are illustrated by numerical examples. Copyright © 2010 John Wiley & Sons, Ltd.     

An in vitro protocol for evaluation and comparison of membrane oxygenators

With the trend in open heart surgery toward normothermic bypass and warm blood cardioplegia, greater demand is being placed on the perfusionist to select an oxygenator that will perform safely and efficiently under a variety of conditions. While manufacturers report performance parameters for their products, the data is often not comparable due to widely differing conditions. Recent in vitro evaluation techniques employed to characterize membrane oxygenators do not simulate the actual oxygenator conditions observed during cardiopulmonary bypass. Biocompatibility and drug delivery are reported but comparisons of different oxygenator performance parameters are not completely addressed. We have designed a test circuit and an evaluation protocol to simultaneously characterize the performance of multiple oxygenators under identical conditions. The test circuit is designed to simulate clinical conditions and to evaluate gas exchange, blood path pressures, gas path pressures, and hemolysis. Previously reported studies have relied on a comparison of a single membrane oxygenator and a single bubble oxygenator. Our protocol will compare multiple membrane oxygenators, in vitro, under similar clinically relevant conditions. Such testing would be done prior to animal or clinical trials. Furthermore in vitro tests should be more reproducible and more discriminating than are ex vivo tests.     

An optimal control problem with nonlocal conditions for the weakly nonlinear hyperbolic equation

Some problems in physics and engineering may be effectively described in terms of nonlocal problems for differential equations. These nonlocal conditions show that some data on the boundary cannot be measured, and therefore some averaged data of the problem are given. In the present paper, necessary conditions of optimality in the optimal control problem are derived for hyperbolic equations with nonlocal boundary conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Rectal prolapse and surgery for faecal incontinence

Both rectal prolapse and faecal incontinence are common, multifactorial conditions that present both electively to colorectal and pelvic floor clinics, and to the emergency take. The conditions can be complex to treat as can the medical conditions of the elderly patients they can affect. Treatments are evolving but will often involve significant buy in from patients and their carers. This article highlights some of these surgical interventions to enable trainees to have discussions in outpatient settings.     

Insights From the Eye for Patients With Kidney Transplant

The eye and the kidney share structural and developmental similarities on a cellular and clinical level, and they are often affected by the same disease processes. Performing an eye exam to look for signs of conditions such as hypertension and diabetes can provide a helpful window into the health of the kidney.Patients with kidney transplants (KT) are a unique population that require close monitoring. These patients are maintained on a number of immunosuppressive medications and may face complications such as medication side effects, infections, and graft rejection. Patients with KT are at higher risk of both infectious and noninfectious eye conditions related to underlying systemic disease or use of immunosuppressive medications.Screening for eye conditions is important because preserving visual function is integral to quality of life, and also because the eye exam can help with early detection and treatment of systemic conditions. Here we describe some of the common eye findings and conditions in patients with KT. We recommend that patients with KT receive annual eye exams, and we hope that the information provided here can help nephrologists become more familiar with eye findings and identify situations where a referral to ophthalmology is warranted.     

Laparoscopy for adhesions

Intestinal and abdominal adhesions may be responsible for a variety of clinical conditions, including chronic recurrent small-bowel obstruction, acute small-bowel obstruction, closed-loop bowel obstruction and, debatably, abdominal or pelvic pain. Experience in laparoscopic surgery has increased at a rapid pace, thus adhesions are no longer considered a contraindication to treatment of these conditions. In recent years, numerous publications have reported the feasibility, safety, and favorable outcome of laparoscopic intervention in various adhesion-related conditions. As adhesions are the most common cause of recurrent or acute bowel obstruction, this review will focus on the laparoscopic management of these conditions and outline the technical considerations, indications, contraindications, and results.     

Diagnostic significance of hypocomplementemia.

Hypocomplementemia is an important marker for the presence of IC-mediated disease and can be used to assess disease activity. However, in interpreting the clinical significance of hypocomplementemia, the following must be kept in mind: 1) There are numerous non-immunologic conditions that also can cause hypocomplementemia. Furthermore, some of these conditions can cause a multisystem disease that, along with the hypocomplementemia, can closely resemble an IC-mediated systemic vasculitis. Furthermore, these nonimmunologic conditions that lower serum complement levels can complicate the course of patients with inactive IC-mediated disease, spuriously indicating that the disease is active. The most relevant of these differential diagnostic problems are listed in Table 2. 2) There are a few conditions (for example, pregnancy) that can raise serum complement levels, thereby possibly obscuring the presence of a disorder (such as, active SLE) that is lowering complement levels. 3) There are some conditions that might be expected to lower serum complement levels, because of their effect on protein metabolism, but do not. Nephrotic syndrome, and moderately poor nutrition are examples. All of these factors should be considered when interpreting results of serum complement levels in a given patient.     

Genetic aspects of orthopedic conditions.

Genetic conditions seen by orthopedists may be divided into Mendelian disorders, chromosome abnormalities and multifactorial conditions. Mendelian disorders involve the abnormality of a single gene and obey the rules of Mendelian inheritance. Chromosome abnormalities are caused by the absence or duplication of a sufficient number of genes to allow this abnormality to be detected by chromosome studies. Chromosome studies are used to confirm the diagnosis of well described syndromes of deletion or trisomy. These studies are also necessary to determine whether mongolism has been caused by non-disjunction or translocation, so that proper genetic counseling can be carried out in these conditions. Multifactorial conditions are determined by several genes or more commonly, by a combination of genetic and environmental factors. These conditions recur in families in a greater incidence than one would expect in the general population but do not obey the rules of Mendelian inheritance. Genetic counseling cannot be performed without an absolute diagnosis, an absolute knowledge of the patterns of inheritance and a well documented family pedigree. The basic principles of genetics covered in this article should allow the orthopedist to understand when genetic counseling is indicated for his patients.     

Radiolucent filling defects of the renal pelvis: classification and report of unusual cases.

Eight cases of unusual radiolucent filling defects in the renal pelvis and calices are reported. With reference to the literature and these cases, such defects have been classified etiologically as tumors, calculi, blood clots, air bubbles, congenital anomalies, vascular phenomena, infections and associated conditions, foreign bodies and miscellaneous conditions. Most of these conditions are rare but their accurate delineation with modern diagnostic techniques will allow for more conservative surgical procedures and for maximal preservation of renal substance.     

Exponential stability analysis for 2D discrete switched systems with state delays

This paper is concerned with the delay‐dependent exponential stability analysis of two‐dimensional (2D) discrete switched systems with state delays described by the Roesser model; the delays under consideration are varying. By constructing an appropriate Lyapunov‐Krasovskii functional and using the average dwell time approach, new delay‐dependent sufficient conditions for the exponential stability of the system under study are proposed. In order to obtain less conservative conditions, the delay partitioning method is adopted as well as the free‐weighting matrix technique. The proposed conditions are formulated in the format of linear matrix inequality. The effectiveness and the reduced conservatism of the developed results are shown by illustrative examples.     

Optimization methods for the verification of second order sufficient conditions for bang–bang controls

It has been common practice to find controls satisfying only necessary conditions for optimality, and then to use these controls assuming that they are (locally) optimal. However, sufficient conditions need to be used to ascertain that the control rule is optimal. Second order sufficient conditions (SSC) which have recently been derived by Agrachev, Stefani, and Zezza, and by Maurer and Osmolovskii, are a special form of sufficient conditions which are particularly suited for numerical verification. In this paper we present optimization methods and describe a numerical scheme for finding optimal bang–bang controls and verifying SSC. A straightforward transformation of the bang–bang arc durations allows one to use standard optimal control software to find the optimal arc durations as well as to check SSC. The proposed computational verification technique is illustrated on three example applications. Copyright © 2005 John Wiley & Sons, Ltd.