bluuebunny/crossref_metadata_2025 huggingface dataset:
Sinus Node Dysfunction After Orthotopic Cardiac Transplantation: Postoperative Incidence and Long‐Term Implications
Authors: HEINZ GOTTFRIED , HIRSCHL MICHAEL , BUXBAUM PETER , LAUFER GÜNTHER , GASIC SLOBODAN , LACZKOVICS AXEL
Published: July 2007

HEINZ, G., et al.: Sinus Node Dysfunction After Orthotopic Cardiac Transplantation: Postoperative Incidence and Long‐Term Implications. We investigated incidence, normalization rates, and clinical significance of sinus node (SN) dysfunction after cardiac transplantation. Thirty‐nine of 90 patients systematically evaluated presented with impaired SN function in the postoperative period. Of these, 22 normalized their SN function during follow‐up while 17 remained impaired after 3 months. The proportion normalized was higher in patients with prolonged SN recovery time (11/16, 68.8%) and those reverting from escape rhythm to sinus rhythm until discharge (5/8, 62.5%) when compared to patients in escape rhythm throughout the postoperative period (5/11, 45.5%) or pacemaker dependence (1/4, 25%). There was no reliable postoperative predictor of normalization and necessity of long‐term pacing. A postoperative heart rate consistently < 70 beats/min (irrespective of the native rhythm) was significantly related to outcome (P = 0.01), but revealed unacceptable sensitivity (61.5%) and specificity (81%). After all, both patients with severe symptoms (near syncopes and syncope), were derived from this group. These two patients, who had been discharged in sinus rhythm, had late pacemakers implanted. An additional 17 patients had early pacemaker placement, only seven of which were constantly paced during follow‐up. Given the low normalization rates, patients with postoperative escape rhythm are those most likely to benefit from pacemaker therapy over the long term. Even those in, or reverting back to, sinus rhythm until discharge may experience severe symptoms, particularly in the setting of a postoperative rate consistently < 70 beats/min since this indicates a relatively lower probability of recovery.
Failure of a Second and Third Generation Implantable Cardioverter Defibrillator to Sense Ventricular Tachycardia: Implications for Fixed‐Gain Sensing Devices
Authors: SPERRY ROBERT E. , ELLENBOGEN KENNETH A. , WOOD MARK A. , STAMBLER BRUCE S. , DiMARCO JOHN P. , HAINES DAVID E.
Published: July 2007

SPERRY, R.E., et al.: Failure of a Second and Third Generation Implantable Cardioverter Defibrillator to Sense Ventricular Tachycardia: Implications for Fixed‐Gain Sensing Devices. Failure to sense ventricular tachycardia and/or ventricular fibrillation by implantable cardioverter defibrillators (ICDs) is rare. We report a case in which persistent undersensing of monomorphic and polymorphic ventricular tachycardia occurred with a second and third generation ICD using fixed‐gain sensing. This occurred despite adequate R wave sensing during sinus rhythm. The use of an endocardial sensing lead did not correct the problem. Failure to sense ventricular tachycardia in the third generation device with fixed‐gain sensing occurred late after implantation and was discovered only at follow‐up electrophysiology testing of the ICD. This problem could not be corrected by reprogramming of the device, and was not related to lead dislodgement. Placement of a new device with an automatic‐gain sensing algorithm and use of previously implanted epicardial leads with better sensing characteristics provided appropriate sensing of ventricular tachyarrhythmias. The case illustrates the importance of testing the sensing of all ventricular arrhythmias in patients with fixed‐gain ICD's. Follow‐up electrophysiology testing and evaluation of epicardial and endocardial leads may be necessary in certain cases to ensure adequate sensing of ventricular tachyarrhythmias late after implantation.
Frequency and Output‐Dependent Change in Conduction Over Slow Pathways in a Patient with Sustained Ventricular Tachycardia Unrelated to Coronary Artery Disease
Authors: CHINUSHI MASAOMI , AIZAWA YOSHIFUSA , FUNAZAKI TOSHIKAZU , TAMURA MAKOTO , SHIBATA AKIRA
Published: July 2007

CHINUSHI, M., et al.: Frequency and Output‐Dependent Change in Conduction Over Slow Pathways in a Patient with Sustained Ventricular Tachycardia Unrelated to Coronary Artery Disease. In a patient with sustained ventricular tachycardia, we obtained two different paced QRS morphologies from a single pacing site. In one QRS morphology the stimulus to the QRS complex was long, 150 msec, and in the other it was 100 msec. At the paced cycle Iength of 600 msec and the stimulus output of 4 V, one QRS morphology with the stimulus to the onset of QRS activation (St‐QRS) interval of 150 msec was observed. At the paced cycle length of 400 msec, the other QRS morphology with a St‐QRS interval of 100 msec was observed alternately with the former. At the paced cycle length of 353 msec or 316 msec, the latter with a shorter St‐QRS interval was exclusively observed. When the stimulus output was increased from 4 to 10 V, keeping with the paced cycle length at 400 msec, the St‐QRS interval was shortened from 100 to 80 msec. For the two QRS morphologies with two St‐QRS intervals, two slowly conducting pathways would be responsible. The site of the block in the faster pathway must be located at the proximity of the pacing site and the conduction at a shorter paced cycle length would be explained by “supernormal conduction.”
Permanent AV Block or Modification of AV Nodal Function by Selective AV Nodal Artery Ethanol Infusion
Authors: WANG PAUL J. , URSELL PHILIP C. , SOSA‐SUAREZ GUILLERMO , OKISHIGE KAORU , FRIEDMAN PETER L.
Published: July 2007

WANG, P.J., et al.: Permanent AV Block or Modification of AV Nodal Function by Selective AV Nodal Artery Ethanol Infusion. The acute and chronic effects of selective AV nodal artery ethanol infusion on AV nodal function was studied in 9 closed chest anesthetized dogs. Using standard percutaneous techniques of arterial catheterization, a 2.2 French infusion catheter was positioned in the AV nodal artery. Ten minute infusions into the AV nodal artery of 25%, 50%, or 100% ethanol in normal saline at rates of 0.5 mL/min acutely resulted in complete AV nodal block (AVE) in 5 dogs, 2:1 AV nodal block in 1 dog, and prolongation of AV nodal effective refractory period and/or Wenckebach cycle length in the remaining 3 dogs. One dog died with persistent complete AV block 1 week after the ethanol infusion. When restudied 4 weeks later, 7 of the 8 surviving dogs had persistent modification of AV nodal function, including complete AV block in 5 dogs and lengthening of AV nodal effective refractory period and/or Wenckebach cycle length without AV block in 2 dogs. Pathologic examination of the animals exhibiting chronic modification or ablation of AV nodal function revealed healing infarction of the AV node or its approaches. Distant myocardial necrosis was not observed and left ventricular function was normal. Slow infusion of low concentrations of ethanol into the AV nodal artery results in AV nodal modification or ablation due to localized necrosis in or around the AV node. This technique may have a role in AV nodal modification or ablation, particularly in patients who have failed DC shock or radiofrequency ablation.
Diagnosis and Localization of Accessory Pathways
Authors: CAIN MICHAEL E. , LUKE ROBERT A. , LINDSAY BRUCE D.
Published: July 2007

The WPW syndrome is a curable disease. The evolution of nonpharmacological methods of accessory pathway ablation has had a significant impact on management strategies in patients with arrhythmias mediated by accessory pathways. Despite an incidence of preexcitation in the general population of 0.1% to 0.3%, curative therapy is underutilized. This review has highlighted the traditional and newer methods of diagnosing and localizing accessory pathways. The number of patients benefiting from definitive therapy will parallel increased physician awareness of these methods.
Tissue Doppler Echocardiography Contribution to the Diagnosis of Upper Extremities Venous Thrombosis
Authors: Lazaros George , Matsakas Evangellos , Karavidas Apostolos , Panou Fotis , Fotiadis Ioannis , Zacharoulis Apostolos
Published: July 2007

We present the case of a 35‐year‐old man with a history of β‐thalassemia complicated with heart failure who was admitted to our department because of right arm painful swelling. A transthoracic echo‐Doppler study revealed a mass within the right jugular vein (RJV) lumen and absence of flow within the right subclavian vein (RSV). Subsequently, color tissue Doppler echocardiography clearly demonstrated the intraluminal mass by means of its different color hues as compared with the surrounding vessel wall, further enforcing the suspicion of upper extremity vein thrombosis (UEVT). It is emphasized that tissue Doppler echocardiography, a safe and reproducible method, can contribute to the diagnosis of UEVT.
Nonobstructive Asymmetrical Septal Hypertrophy and Ostium Secundum‐Type Atrial Septal Defect
Authors: Hernandez‐Reyes Pablo , Espinola‐Zavaleta Nilda , Vargas‐Barron Jesus , Romero‐Cardenas Angel , Roldan‐Gomez Javier , Keirns Candace
Published: July 2007

We report a 36‐year‐old woman with hypertrophic cardiomyopathy with asymmetric septal hypertrophy without outflow tract obstruction associated with an ostium secundum‐type atrial septal defect with significant hemodynamic repercussion. Diagnosis was established with transesophageal echocardiography. This is the second case of this rare association reported in the literature and the first evaluated by transesophageal echocardiography.
Occludin is overexpressed in Alzheimer's disease and vascular dementia
Authors: Romanitan Mihaela Oana , Popescu Bogdan O. , Winblad Bengt , Bajenaru Ovidiu Alexandru , Bogdanovic Nenad
Published: July 2007

The tight junctions (TJs) are key players in the control of blood‐brain barrier (BBB) properties, the most complex TJs in the vascular system being found in the endothelial cells of brain capillaries. One of the main TJs proteins is occludin, which anchors plasma membranes of neighbour cells and is present in large amounts in the brain endothelia. Previous studies demonstrated that disruption of BBB in various pathological situations associates with changes in occludin expression, and this change could be responsible for malfunction of BBB. Therefore in this study, applying an immunohistochemical approach, we decided to explore the occludin expression in frontal cortex (FC) and basal ganglia in ageing control, Alzheimer's disease (AD), and vascular dementia (VD) brains, as far as all these pathologies associate microangiopathy and disruption of BBB. Strikingly, we found selected neurons, astrocytes and oligodendrocytes expressing occludin, in all cases studied. To estimate the number of occludin‐expressing neurons, we applied a stereological approach with random systematic sampling and the unbiased optical fractionator method. We report here a significant increase in ratio of occludin‐expressing neurons in FC and basal ganglia regions in both AD and VD as compared to ageing controls. Within the cerebral cortex, occludin was selectively expressed by pyramidal neurons, which are the ones responsible for cognitive processes and affected by AD pathology. Our findings could be important in unravelling new pathogenic pathways in dementia disorders and new functions of occludin and TJs.
Alzheimer's Disease: cholesterol, membrane rafts, isoprenoids and statins
Authors: Reid Patrick C. , Urano Yasuomi , Kodama Tatsuhiko , Hamakubo Takao
Published: July 2007

Introduction

Conclusions

Alzheimer's disease (AD) is a heterogeneous neurodegenerative disorder and the most prevalent form of dementia worldwide. AD is characterized pathologically by amyloid‐β plaques, neurofibrillary tangles and neuronal loss, and clinically by a progressive loss of cognitive abilities. At present, the fundamental molecular mechanisms underlying the disease are unclear and no treatment for AD is known. Epidemiological evidence continues to mount linking vascular diseases, such as hypertension and diabetes, and hypercholesterolaemia with an increased risk for developing AD. A growing amount of evidence suggests a mechanistic link between cholesterol metabolism in the brain and the formation of amyloid plaques in AD development. Cholesterol and statins clearly modulate β‐amyloid precursor protein (βAPP) processing in cell culture and animal models. Statins not only reduce endogenous cholesterol synthesis but also exert other various pleiotrophic effects, such as the reduction in protein isoprenylation. Through these effects statins modulate a variety of cellular functions involving both cholesterol (and membrane rafts) and isoprenylation. Although clearly other factors, such as vascular inflammation, oxidative stress and genetic factors, are intimately linked with the progression of AD, this review focuses on the present research findings describing the effect of cholesterol, membrane rafts and isoprenylation in regulating βAPP processing and in particular γ‐secretase complex assembly and function and AD progression, along with consideration for the potential role statins may play in modulating these events.
Primary desminopathies
Authors: Schröder Rolf , Vrabie Alexandra , Goebel Hans H.
Published: July 2007

Introduction

Desmin is an essential component of the extrasarcomeric cytoskeleton in striated muscle cells

Distal myopathy,cardiac arrhythmias,cardiomyopathy:classical criteria of primary desminopathies

Sub‐sarcolemmal and cytoplasmic desmin‐positive protein aggregates:the morphological hallmark of primary and secondary desminopathies

The spectrum of pathogenic desmin gene mutations

The molecular pathogenesis of primary desminopathies: some answers gained,but even more questions raised

Diagnostic work‐up to distinguish primary from secondary desminopathies

Treatment and clinical management of primary desminopathy patients

Mutations of the human desmin gene on chromosome 2q35 cause a familial or sporadic form of skeletal myopathy frequently associated with cardiac abnormalities. Skeletal and cardiac muscle from patients with primary desminopathies characteristically display cytoplasmic accumulation of desmin‐immunoreactive material and myofibrillar changes. However, desmin‐positive protein aggregates in conjunction with myofibrillar abnormalities are also the morphological hallmark of the large group of secondary desminopathies (synonyms: myofibrillar myopathies, desmin‐related myopathies), which comprise sporadic and familial neuromuscular conditions of considerable clinical and genetic heterogeneity. Here, we will give an overview on the functional role of desmin in striated muscle as well as the main clinical, myopathological, genetic and patho‐physiological aspects of primary desminopathies. Furthermore, we will discuss recent genetic and biochemical advances in distinguishing primary from secondary desminopathies.
The end of the Union?
Authors: Lodge Guy , Schmuecker Katie
Published: July 2007

Gordon Brown has made clear that his first hundred days will see a major new push on the constitutional front. Guy Lodge and Katie Schmuecker argue that addressing the tensions within the Union between England and Scotland must play a central role in any reform agenda.
Harm and hypocrisy
Authors: Wolff Jonathan
Published: July 2007

The regulation of recreational drugs makes no philosophical sense, argues Jonathan Wolff, but, in bringing their perspective to public policy debates, philosophers have to do more than start from a position that is abstracted from day‐to‐day reality.
Research with Human Subjects as a Paradigm in Teaching
Authors: Palmer Larry I.
Published: July 2007

As a university administrator, I worry about the form and substance of undergraduate education and about ways to encourage interdisciplinary perspectives on problems in a research university dominated by particular specialized disciplines. I also continue to teach a seminar in Cornell's Biology & Society Program for undergraduates and to assist others in teaching a course called Medical Humanities for second-year medical students. In the course of these administrative and teaching activities, I find myself returning to Jay Katz's Experimentation with Human Beings —both as model for teaching and as a perspective for institutional learning and change —as a model for professional action.

Jay Katz's approach to research with human subjects provides an excellent framework for analyzing the nature of teaching not simply in professional or continuing education programs in law, medicine, or social work, but in undergraduate programs as well. In my view, changing the ways in which universities help students to learn at all levels can be analyzed through the process of reflection, action, and evaluation developed in Katz's seminal work on human experimentation and most recently expounded in his suggested reforms of professional medical education in The Silent World of Doctor and Patient. For Jay Katz, the scholar who guided me to the realization that teaching and administering within the university at all levels is essentially a problem in human research, I offer this tribute.
A Psychiatrist on the Law School Faculty: Influences on Professional Careers
Authors: Watson Andrew S.
Published: July 2007

I feel it a great honor to be invited to participate in the development of this festschrift for my old and dear friend, Jay Katz. We have shared the interdisciplinary trenches from the very beginning of our respective careers. We have struggled with some of the same problems; we have sometimes joined in teaching projects; there are several areas of law that we have both explored; and on one occasion we have even opposed each other as expert witnesses. Throughout the duration of these thirty-three years I have followed Jay's work closely, fully agreed with most of his principles, and often felt a twinge of envy that I had not written some of the papers which he did. Likewise, I have always felt greatly supported by Jay in my efforts, even though we have had minor disagreements from time to time and I shall discuss one of these later on. I seriously doubt that Jay's most recent works will turn out to be truly a valedictory. I anticipate the pleasure of continuing to read stimulating pieces by him in future years.
Research Involving Humans: A Time for Change?
Authors: Chalmers Don
Published: July 2007

Amongst Professor Dickens’ extensive writings on medical law and medical jurisprudence are a host of distinguished contributions on the subject of the proper legal and ethical limits on human experimentation. As early as 1975, Professor Dickens was examining the legal aspects of human experimentation. A few years later he was promoting the responsibility of researchers to recognize and protect human rights in medical experimentation. In the last two decades, Professor Dickens has penned a rich flow of scholarly contributions on the legal and ethical rights and duties in medical experimentation and the need to do better as a research community. His articles have considered a broad range of issues in medical experimentation including the imperative of voluntary consent, the ethical unacceptability of co-ercion or inducement of research participants, embryonic research, epidemiological research and the protection of vulnerable research participants, particularly children.
Institutional Conflicts of Interest: Protecting Human Subjects, Scientific Integrity, and Institutional Accountability
Authors: DuVal Gordon
Published: July 2007

If clinical trials become a commercial venture in which self-interest overrules public interest and desire overrules science, then the social contract which allows research on human subjects in return for medical advances is broken.

Background

In the past two decades, the involvement of non-academic sponsors of biomedical research, particularly clinical trial research, has increased exponentially. The value of such sponsored research is difficult to ascertain. However, it is estimated that, between 1980 and 2003, overall research and development expenditures by US pharmaceutical companies increased from $2 billion to $33 billion and that, in 2001, clinical trial research expenditures in Canada totaled $800 million to $1 billion.

The source of funding for biomedical research has shifted significantly from predominantly government and private foundations to industry. By 2002,70% of funding for clinical trials came from industry. These factors have affected the conduct of research, particularly clinical trial research, in a variety of ways.
Legal and Ethical Approaches to Stem Cell and Cloning Research: A Comparative Analysis of Policies in Latin America, Asia, and Africa
Authors: Isasi Rosario M. , Knoppers Bartha M. , Singer Peter A. , Daar Abdallah S.
Published: July 2007

Human reproductive cloning has become the most palpable example of the globalization of science. Throughout the world, events and conjectures in the media, such as the birth and death in the United Kingdom of the cloned sheep Dolly and projects to clone human beings by Korean scientists, by members of the Canadian-based Raelian cult, and by the Italian physician Antinori in an undisclosed country, have galvanized the political will of individual countries to ban human reproductive cloning.

Yet, international attempts to harmonize policies in the area of biomedical ethics and human research, such as the 1997 Council of Europe’s Convention on Human Rights and Biomedicine, and most recently, the United Nations’ efforts to adopt an international convention against human reproductive cloning, have been insufficient to trigger a substantial global policy design process on issues relating to these new technologies.
Leopards in the Temple: Restoring Scientific Integrity to the Commercialized Research Scene
Authors: Lemmens Trudo
Published: July 2007

Leopards break into the temple and drink to the dregs what is in the sacrificial pitchers; this is repeated over and over again; finally it can be calculated in advance, and it becomes part of the ceremony.

–Franz Kafla

For more than two decades, significant controversies have been brewing over the efficacy and safety of Selective Serotonin Reuptake Inhibitors (or SSRIs) and other treatments for depression, and also over the expansion of their use for the treatment of a variety of other conditions. These controversies culminated, in June 2004, with alawsuit intended by Eliot Spitzer, Attorney General of the State of New York. The lawsuit accused pharmaceutical giant GlaxoSmith-Kline of “repeated and persistent fraud by misrepresentation, concealing and otherwise failing to disclose to physicians information in its control concerning the safety and effectiveness of its antidepressant medication paroxetine” (better known as “Paxil”) in treating children and adolescents suffering from depression.
The Changing Legal and Conceptual Shape of Health Care Privacy
Authors: Magnusson Roger S.
Published: July 2007

The contributions of Professor Bernard Dickens to health law and bioethics span the era in which these fields have emerged as distinct domains of teaching, scholarship and professional and public conversation. Neither field exists in a vacuum. The concerns of bioethics, like the content of health law, are a product of social forces. The bureaucratization of medical care, the possibilities and uncertainties created by developments in medical technology, not to mention glaring health inequalities, have been destabilizing forces in medicine. Writing in 1974, American sociologist Renée Fox noted that medicine had reached “a stage of development characterized by diffuse ethical and existential self-consciousness.” This new medical introspection was evidenced by intense engagement with issues of biomedical regulation, and with the growth of professional codes and processes for resolving value-laden issues within clinical settings.

While sometimes described as a process or site for discussion and “engagement,” bioethics evolved rapidly into a domain of governance, with direct implications for clinical practice.
An Appraisal of Abortion Laws in Southern Africa from a Reproductive Health Rights Perspective
Authors: Ngwena Charles
Published: July 2007

The World Conference on Human Rights (the Vienna Conference) that was held in Vienna in 1993, marked an important beginning in the recognition of reproductive and sexual rights as human rights. Among other goals, the Vienna Conference sought to end gender discrimination in all its manifestations; gender-based violence, sexual harassment, and sexual exploitation. However, the turning point for the development of reproductive and sexual rights was the consensus that emanated from the International Conference on Population and Development held in Cairo in 1994 (the Cairo Conference), and the Fourth World Conference on Women in held in Beijing 1995 (the Beijing Conference) as evidenced by the programs for action that were adopted.

The Cairo Conference defined reproductive health as “a state of complete physical, mental and social well-being and not merely the absence of infirmity, in all matters relating to the reproductive system and to its functions and processes.”
What Conditions Justify Risky Nontherapeutic or “No Benefit” Pediatric Studies: A Sliding Scale Analysis
Authors: Kopelman Loretta M.
Published: July 2007

Many pediatric research regulations, including those of the United States, the Council for International Organizations of Medical Science (CIOMS), and South Africa, offer similar rules for review board approval of higher hazard studies holding out no therapeutic or direct benefit to children with disorders or conditions (See Table 1). Authorization requires gaining parental permissions and the children’s assent, if that is possible, and showing that these studies are intended to gain vitally important and generalizable information about children’s conditions; it also requires limiting the risks of harm to no more than a “minor increase over minimal risk” and showing the study is commensurable with the children’s experiences. For convenience, these investigations will be called “no benefit, higher hazard” studies.

Despite the existence of these policies for decades, studies show that review boards’ judgments vary about what “no benefit, higher hazard” studies should be approved.
Bladder afferent sensitivity in wild‐type and TRPV1 knockout mice
Authors: Daly D. , Rong W. , Chess‐Williams R. , Chapple C. , Grundy D.
Published: July 2007

Understanding bladder afferent pathways may reveal novel targets for therapy of lower urinary tract disorders such as overactive bladder syndrome and cystitis. Several potential candidate molecules have been postulated as playing a significant role in bladder function. One such candidate is the transient receptor potential vanilloid 1 (TRPV1) ion channel. Mice lacking the TRPV1 channel have altered micturition thresholds suggesting that TRPV1 channels may play a role in the detection of bladder filling. The aim of this study was therefore to investigate the role of TRPV1 receptors in controlling bladder afferent sensitivity in the mouse using pharmacological receptor blockade and genetic deletion of the channel. Multiunit afferent activity was recorded in vitro from bladder afferents taken from wild‐type (TRPV+/+) mice and knockout (TRPV1−/−) mice. In wild‐type preparations, ramp distension of the bladder to a maximal pressure of 40 mmHg produced a graded increase in afferent activity. Bath application of the TRPV1 antagonist capsazepine (10 μm) caused a significant attenuation of afferent discharge in TRPV1+/+ mice. Afferent responses to distension were significantly attenuated in TRPV1−/− mice in which sensitivity to intravesical hydrochloric acid (50 mm) and capsaicin (10 μm) were also blunted. Altered mechanosensitivity occurred in the absence of any changes in the pressure–volume relationship during filling indicating that this was not secondary to a change in bladder compliance. Single‐unit analysis was used to classify individual afferents into low‐threshold and high‐threshold fibres. Low threshold afferent responses were attenuated in TRPV1−/− mice compared to the TRPV1+/+ littermates while surprisingly high threshold afferent sensitivity was unchanged. While TRPV1 channels are not considered to be mechanically gated, the present study demonstrates a clear role for TRPV1 in the excitability of particularly low threshold bladder afferents. This suggests that TRPV1 may play an important role in normal bladder function.
Effect of Blade
Passage Surface Heat Extraction on Axial Compressor
Performance
Authors: Shah P.
N. , Tan C.
S.
Published: July 2007

Axial compressor performance with heat extraction via blade passage surfaces (compressor cooling) is compared to its adiabatic counterpart, using computational experiments and mean line modeling. For a multistage compressor with an adiabatic design point, results at fixed corrected rotor speed indicate that, if available, compressor cooling would (i) raise the overall pressure ratio (at a given corrected flow), (ii) raise the maximum mass flow capability, (iii) raise the efficiency, defined as the ratio of isentropic work for a given pressure ratio to actual shaft work, and (iv) provide rear stage choking relief at low corrected speed. In addition, it is found that, if available, cooling in the front stages is better than in the rear stages. This is primarily a thermodynamic effect that results from the fact that, for a given gas, the compression work required to achieve a given pressure ratio decreases as the gas becomes colder. Heat transfer considerations indicate that the engineering challenges lie in achieving high enough heat transfer rates to provide a significant impact to the compressor’s performance.
The Mixed Mode I and II Interface Crack in Piezoelectromagneto–Elastic Anisotropic Bimaterials
Authors: Li R. , Kardomateas G. A.
Published: July 2007

Taking the electric–magnetic field inside the interface crack into account, the interface crack problem of dissimilar piezoelectromagneto (PEMO)–elastic anisotropic bimaterials under in-plane deformation is investigated. The conditions to decouple the in-plane and anti-plane deformation is presented for PEMO–elastic biaterials with a symmetry plane. Using the extended Stroh’s dislocation theory of two-dimensional space and the analytic continuition principle of complex analysis, the interface crack problem is turned into a nonhomogeneous Hilbert equation in matrix notation. Four possible eigenvalues as well as four eigenvectors for the fundamental solution to the corresponding homogeneous Hilbert equation are found, so are four modes of singularities for the fields around the interface crack tip. These singularities are shown to have forms of r−(1∕2)±iϵ1 and r−(1∕2)±iϵ2, in which the bimaterial constants ϵ1 and ϵ2 are proven to be real numbers for practical dissimilar PEMO–elastic bimaterials. Compared with the solution for the interface crack of dissimilar elastic bimaterials without electro–magnetic properties, two new additional singularities are discovered for the interface crack in the PEMO–elastic bimaterial media. The electric–magnetic field inside the crack is solved by employing the “energy method,” which is based on finding the stationary point of the saddle surface of the energy release rate with respect to the electro–magnetic field inside the crack. Closed form expressions for the extended crack tip stress fields and crack open displacements are formulated, so are some other fracture characteristic parameters, such as the extended stress intensity factors and energy release rate (G) for dissimilar PEMO–elastic bimaterial solids. Finally, fundamental results and some conclusions are presented, which could have applications in the failure of piezoelectro/magneto–elastic devices.
Dynamic Compressive Response of Stainless-Steel Square Honeycombs
Authors: Radford D. D. , McShane G. J. , Deshpande V. S. , Fleck N. A.
Published: July 2007

The dynamic out-of-plane compressive response of stainless-steel square honeycombs has been investigated for impact velocities ranging from quasi-static values to 300ms−1. Square-honeycomb specimens of relative density 0.10 were manufactured using a slotting technique, and the stresses on the front and back faces of the dynamically compressed square honeycombs were measured using a direct impact Kolsky bar. Three-dimensional finite element simulations of the experiments were performed to model the response and to help interpret the experimental results. The study has identified three distinct factors governing the dynamic response of the square honeycombs: material rate sensitivity, inertial stabilization of the webs against buckling, and plastic wave propagation. Material rate sensitivity and inertial stabilization of the webs against buckling cause the front and back face stresses to increase by about a factor of two over their quasi-static value when the impact speed is increased from 0 to 50ms−1. At higher impact velocities, plastic wave effects cause the front face stress to increase linearly with velocity whereas the back face stress is almost independent of velocity. The finite element predictions are in reasonable agreement with the measurements.
Transient Response of Tapered Elastic Bars
Authors: Chicone Carmen , Heitzman Michael , Feng Z. C.
Published: July 2007

Exact solutions are obtained for a model of the longitudinal displacement along an elastic tapered bar due to a force applied at its blunt end. A formula for velocity amplification is given; it specifies the velocity of the pointed end of the bar shortly after it feels the influence of the force. For a bar with an exponentially decreasing cross-sectional area, the velocity is magnified by twice an exponential function of length. This result has applications in the design of piezoelectric drills. In addition, we discuss the differences between the motions of rigid and elastic bars during the transient before one complete reflection of the wave induced by a force applied to an end of the bar. In this regime, force is proportional to velocity for elastic bars with constant cross-sectional areas. While the force–velocity relationship is more complicated for tapered elastic bars, their exact relationship is determined.
Optimization of a Real-Time Simulator Based on Recurrent Neural Networks for Compressor Transient Behavior Prediction
Authors: Venturini M.
Published: July 2007

In this paper, feed-forward recurrent neural networks (RNNs) with a single hidden layer and trained by using a back-propagation learning algorithm are studied and developed for the simulation of compressor behavior under unsteady conditions. The data used for training and testing the RNNs are both obtained by means of a nonlinear physics-based model for compressor dynamic simulation (simulated data) and measured on a multistage axial-centrifugal small-size compressor (field data). The analysis on simulated data deals with the evaluation of the influence of the number of training patterns and of each RNN input on model response, both for data not corrupted and corrupted with measurement errors, for different RNN configurations, and different values of the total delay time. For RNN models trained directly on experimental data, the analysis of the influence of RNN input combination on model response is repeated, as carried out for models trained on simulated data, in order to evaluate real system dynamic behavior. Then, predictor RNNs (i.e., those that do not include among the inputs the exogenous inputs evaluated at the same time step as the output vector) are developed and a discussion about their capabilities is carried out. The analysis on simulated data led to the conclusion that, to improve RNN performance, the adoption of a one-time delayed RNN is beneficial, with an as-low-as-possible total delay time (in this paper, 0.1s) and trained with an as-high-as possible number of training patterns (at least 500). The analysis of the influence of each input on RNN response, conducted for RNN models trained on field data, showed that the single-step-ahead predictor RNN allowed very good performance, comparable to that of RNN models with all inputs (overall error for each single calculation equal to 1.3% and 0.9% for the two test cases considered). Moreover, the analysis of multi-step-ahead predictor capabilities showed that the reduction of the number of RNN calculations is the key factor for improving its performance over a significant time horizon. In fact, when a high test data sampling time is chosen (in this paper, 0.24s), prediction errors were acceptable (lower than 1.9%).
Development of a One-Dimensional Modular Dynamic Model for the Simulation of Surge in Compression Systems
Authors: Morini M. , Pinelli M. , Venturini M.
Published: July 2007

The paper deals with the development of a nonlinear one-dimensional modular dynamic model for the simulation of transient behavior of compression systems. The model is based on balance equations of mass, momentum, and energy, which are derived through a general approach and are written by using the finite difference method. The model also takes rotating mass dynamics into account through a lumped parameter approach. Moreover, it reproduces the behavior of the system in the presence of the surge phenomenon through steady-state performance maps, which represent the compressor operation in the inverse flow region by means of a third degree polynomial curve. The model is implemented through the Matlab Simulink tool, where the system of ordinary differential equations is solved by using a fourth- and fifth-order Runge–Kutta method. A sensitivity analysis is carried out to evaluate the influence on compressor outlet pressure oscillations of the model parameters, of the supplied torque, of ambient conditions and of the shape of the compressor characteristic curves. The results show that the model proves effective in capturing the physical essence of surge phenomenon without being computationally too heavy.
Investigation of the Flow Field in a High-Pressure Turbine Stage for Two Stator-Rotor Axial Gaps—Part I: Three-Dimensional Time-Averaged Flow Field
Authors: Gaetani P. , Persico G. , Dossena V. , Osnaghi C.
Published: July 2007

An extensive experimental analysis on the subject of unsteady flow field in high-pressure turbine stages was carried out at the Laboratorio di Fluidodinamica delle Macchine (LFM) of Politecnico di Milano. The research stage represents a typical modern HP gas turbine stage designed by means of three-dimensional (3D) techniques, characterized by a leaned stator and a bowed rotor and operating in high subsonic regime. The first part of the program concerns the analysis of the steady flow field in the stator-rotor axial gap by means of a conventional five-hole probe and a temperature sensor. Measurements were carried out on eight planes located at different axial positions, allowing the complete definition of the three-dimensional flow field both in absolute and relative frame of reference. The evolution of the main flow structures, such as secondary flows and vane wakes, downstream of the stator are here presented and discussed in order to evidence the stator aerodynamic performance and, in particular, the different flow field approaching the rotor blade row for the two axial gaps. This results set will support the discussion of the unsteady stator-rotor effects presented in Part II (Gaetani, P., Persico, G., Dossena, V., and Osnaghi, C., 2007, ASME J. Turbomach., 129(3), pp. 580–590). Furthermore, 3D time-averaged measurements downstream of the rotor were carried out at one axial distance and for two stator-rotor axial gaps. The position of the probe with respect to the stator blades is changed by rotating the stator in circumferential direction, in order to describe possible effects of the nonuniformity of the stator exit flow field downstream of the stage. Both flow fields, measured for the nominal and for a very large stator-rotor axial gap, are discussed, and results show the persistence of some stator flow structures downstream of the rotor, in particular, for the minimum axial gap. Finally, the flow fields are compared to evidence the effect of the stator-rotor axial gap on the stage performance from a time-averaged point of view.
Influence of Sweep on
Axial Flow Turbine Aerodynamics at Midspan
Authors: Pullan Graham , Harvey Neil W.
Published: July 2007

Sweep, when the stacking axis of the blade is not perpendicular to the axisymmetric streamsurface in the meridional view, is often an unavoidable feature of turbine design. Although a high aspect ratio swept blade can be designed to achieve the same pressure distribution as an unswept design, this paper shows that the swept blade will inevitably have a higher profile loss. A modified Zweifel loading parameter, taking sweep into account, is first derived. If this loading coefficient is held constant, it is shown that sweep reduces the required pitch-to-chord ratio and thus increases the wetted area of the blades. Assuming fully turbulent boundary layers and a constant dissipation coefficient, the effect of sweep on profile loss is then estimated. A combination of increased blade area and a raised pressure surface velocity means that the profile loss rises with increasing sweep. The theory is then validated using experimental results from two linear cascade tests of highly loaded blade profiles of the type found in low-pressure aeroengine turbines: one cascade is unswept, the other has 45deg of sweep. The swept cascade is designed to perform the same duty with the same loading coefficient and pressure distribution as the unswept case. The measurements show that the simple method used to estimate the change in profile loss due to sweep is sufficiently accurate to be a useful aid in turbine design.
Kinking of Transversal Interface Cracks Between Fiber and Matrix
Authors: París Federico , Correa Elena , Mantič Vladislav
Published: July 2007

Under loads normal to the direction of the fibers, composites suffer failures that are known as matrix or interfiber failures, typically involving interface cracks between matrix and fibers, the coalescence of which originates macrocracks in the composite. The purpose of this paper is to develop a micromechanical model, using the boundary element method, to generate information aiming to explain and support the mechanism of appearance and propagation of the damage. To this end, a single fiber surrounded by the matrix and with a partial debonding is studied. It has been found that under uniaxial loading transversal to the fibers direction the most significant phenomena appear for semidebonding angles in the interval between 60deg and 70deg. After this interval the growth of the crack along the interface is stable (energy release rate (ERR) decreasing) in pure Mode II, whereas it is plausibly unstable in mixed mode (dominated by Mode I for semidebondings smaller than 30deg) until it reaches the interval. At this interval the direction of maximum circumferential stress at the neighborhood of the crack tip is approximately normal to the applied load. If a crack corresponding to a debonding in this interval leaves the interface and penetrates into the matrix then: (a) the growth through the matrix is unstable in pure Mode I; (b) the value of the ERR reaches a maximum (in comparison with other debonding angles); and (c) the ERR is greater than that released if the crack continued growing along the interface. All this suggests that it is in this interval of semidebondings (60-70deg) that conditions are most appropriate for an interface crack to kink. Experiments developed by the authors show an excellent agreement between the predictions generated in this paper and the evolution of the damage in an actual composite.
Analytical Derivation
of Cosserat Moduli via Homogenization of Heterogeneous Elastic
Materials
Authors: Bigoni D. , Drugan W.
J.
Published: July 2007

Why do experiments detect Cosserat-elastic effects for porous, but not for stiff-particle-reinforced, materials? Does homogenization of a heterogeneous Cauchy-elastic material lead to micropolar (Cosserat) effects, and if so, is this true for every type of heterogeneity? Can homogenization determine micropolar elastic constants? If so, is the homogeneous (effective) Cosserat material determined in this way a more accurate representation of composite material response than the usual effective Cauchy material? Direct answers to these questions are provided in this paper for both two- (2D) and three-dimensional (3D) deformations, wherein we derive closed-form formulae for Cosserat moduli via homogenization of a dilute suspension of elastic spherical inclusions in 3D (and circular cylindrical inclusions in 2D) embedded in an isotropic elastic matrix. It is shown that the characteristic length for a homogeneous Cosserat material that best mimics the heterogeneous Cauchy material can be derived (resulting in surprisingly simple formulae) when the inclusions are less stiff than the matrix, but when these are equal to or stiffer than the matrix, Cosserat effects are shown to be excluded. These analytical results explain published experimental findings, correct, resolve and extend prior contradictory theoretical (mainly numerical and limited to two-dimensional deformations) investigations, and provide both a general methodology and specific results for determination of simple higher-order homogeneous effective materials that more accurately represent heterogeneous material response under general loading conditions. In particular, it is shown that no standard (Cauchy) homogenized material can accurately represent the response of a heterogeneous material subjected to a uniform plus linearly varying applied traction, while a homogenized Cosserat material can do so (when inclusions are less stiff than the matrix).
Stochastic Finite Element Buckling Analysis of Laminated Plates With Circular Cutout Under Uniaxial Compression
Authors: Onkar A. K. , Upadhyay C. S. , Yadav D.
Published: July 2007

A generalized stochastic buckling analysis of laminated composite plates, with and without centrally located circular cutouts having random material properties, is presented under uniaxial compressive loading. In this analysis, the layerwise plate model is used to solve both prebuckling and buckling problems. The stochastic analysis is done based on mean centered first-order perturbation technique. The mean buckling strength of composite plates is validated with results available in the literature. It has been observed that the present analysis can predict buckling load accurately even for plates with large cutouts. Micromechanics based approach is used to study the effect of variation in microlevel constituents on the effective macrolevel properties like elastic moduli. Consequently, the effect of uncertainty in these material properties on the buckling strength of the laminated plates is studied. Parametric studies are carried out to see the effect of hole size, layups, and boundary conditions on the mean and variance of plate buckling strength.
Mass Distribution Effects on Dynamic Performance of a Cable-Driven Hexapod
Authors: Bowling Alan P.
Published: July 2007

This paper illustrates the use of dynamic performance analysis in the design of legged robots, specifically hexapods. This is accomplished by comparing the dynamic performance of a cable-driven hexapod to that of a more conventional design in which the actuators are mounted at the joints. By integrating the actuators into the torso and through the use of cable transmission, the mass and inertias of the legs are reduced in order to attain high accelerations and backdrivability. The dynamic performance described herein is bounded by the actuator torque limits and the no-slip condition at the ground contact points. The result is a description of how well each hexapod can accelerate its torso without causing slippage at the ground contact points.