bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial distribution of canine faeces in Buenos Aires suburbs: implications for public health
Authors: Milkovic Mayra , Carbajo Aníbal E , Rubel Diana
Published: December 2008

Canine faecal contamination contributes to environmental degradation and increases the exposure of humans – mainly children – to helminth infections. We studied the magnitude and spatial distribution of faecal contamination on the pavements of two neighbourhoods representative of Buenos Aires suburbs. The pavements of a low‐income neighbourhood (LIN) and a middle‐income neighbourhood (MIN) were selected at random. Field maps including all substrates and objects observed on each pavement were drawn, viewed from above, on millimetre paper at 1:100 scale. Data were then loaded into a geographic information system (GIS) Arc View 3.1 with a digitiser board. The spatial distribution of faeces and its association with substrates or standing elements were analysed at three scales: substrate, pavement and neighbourhood.

Permeable substrate cover was higher in LIN (75%) than in MIN (35%). The faeces were not homogeneously distributed on the substrates. In both neighbourhoods, the substrates with >50 per cent grass cover showed a significantly higher proportion of faeces than those with <50 per cent grass cover, bare soil and tile. At pavement scale, the number of faeces on pavements was not related to either the number of trees, posts and domiciled dogs in the block, or with the number of faeces and percentage cover of each substrate. At patch scale, substrate patches with faeces were larger than those without faeces. Patches with faeces did not differ in shape between neighbourhoods and were more regularly shaped than patches without faeces.

The spatial distribution of faeces relative to each other was almost random, even when analysed in relation to trees or standing objects. Strategies for the sustainable control of this problem are suggested.
Seletracetam (ucb 44212) inhibits high‐voltage–activated Ca2+ currents and intracellular Ca2+ increase in rat cortical neurons in vitro
Authors: Martella Giuseppina , Bonsi Paola , Sciamanna Giuseppe , Platania Paola , Madeo Graziella , Tassone Annalisa , Cuomo Dario , Pisani Antonio
Published: December 2008

Purpose:  We analyzed the effects of seletracetam (ucb 44212; SEL), a new antiepileptic drug candidate, in an in vitro model of epileptic activity. The activity of SEL was compared to the effects of levetiracetam (LEV; Keppra), in the same assays.

Methods:  Combined electrophysiologic and microfluorometric recordings were performed from layer V pyramidal neurons in rat cortical slices to study the effects of SEL on the paroxysmal depolarization shifts (PDSs), and the simultaneous elevations of intracellular Ca2+ concentration [Ca2+]i. Moreover, the involvement of high‐voltage activated Ca2+ currents (HVACCs) was investigated by means of patch‐clamp recordings from acutely dissociated pyramidal neurons.

Results:  SEL significantly reduced both the duration of PDSs (IC50 = 241.0 ± 21.7 nm) as well as the number of action potentials per PDS (IC50 = 82.7 ± 9.7 nm). In addition, SEL largely decreased the [Ca2+]i rise accompanying PDSs (up to 75% of control values, IC50 = 345.0 ± 15.0 nm). Furthermore, SEL significantly reduced HVACCs in pyramidal neurons. This effect was mimicked by ω‐conotoxin GVIA and, to a lesser extent, by ω‐conotoxin MVIIC, blockers of N‐ and Q‐type HVACC, respectively. The combination of these two toxins occluded the action of SEL, suggesting that N‐type Ca2+ channels, and partly Q‐type subtypes are preferentially targeted.

Conclusions:  These results demonstrate a powerful inhibitory effect of SEL on epileptiform events in vitro. SEL showed a higher potency than LEV. The effective limitation of [Ca2+]i influx might be relevant for its antiepileptic efficacy and, more broadly, for pathologic processes involving neuronal [Ca2+]i overload.
Globalization and Economic Development: Impact of Social Capital and Institutional Building
Authors: Cheng Ming Yu , Mittelhammer Ron
Published: December 2008

Abstract

Countries engaged actively in globalization have experienced phenomenal changes in economic, social, cultural, political, and technological progress. Some countries have benefited significantly from greater integration, while others have held globalization accountable for their economic failure and instability. Globalization introduces new political and social challenges. Benefiting from globalization requires complementary institutions and social development to deal with the changes and risks introduced by greater openness. This article examines whether globalization benefits economic development and how the developing countries could gain from globalization through their social capital and institutional building.
Entrepreneurial Culture and Economic Growth: Revisiting McClelland's Thesis
Authors: Beugelsdijk Sjoerd , Smeets Roger
Published: December 2008

Abstract

We reestimate McClelland's (1961) thesis on entrepreneurial culture and economic development. McClelland found a strong positive correlation between measures of need for achievement (N achievement) imagery in school textbooks and the subsequent rate of economic growth. Benchmarking our findings against generally accepted empirical growth models, we find no support for his thesis. This leads us to rethink the relationship between entrepreneurial culture and economic growth.
The Evolution of the Allied Social Science Associations
Authors: Clary Betsy Jane
Published: December 2008

Abstract

The organization of the meetings of the approximately 50 economics associations of the Allied Social Science Associations has evolved over the past 140 years, beginning with meetings of the American Social Science Association in 1865, which included social scientists from political science, history, sociology, and economics. Out of this association, the separate disciplines formed their own organizations beginning in the 1880s. Though several of these associations continued to meet together until the 1930s, each discipline gradually separated its meetings from those of the others. During the 1940s, however, other newly formed economics associations began meeting at the same time and place as the AEA, and the Allied Social Science Associations evolved out of these meetings. Though the name of the organization includes “social science,” the associations meeting together are predominately, if not completely, economics associations. These associations, however, profess many different approaches to the study of economics. This paper traces the evolution of these meetings and attempts to come to some conclusions concerning the significance of this association, the most important of which is the role of the ASSA in providing a broad and tolerant platform and a vehicle through which different points of view toward economic theory and policy can be discussed.
A Brief History of the American Economic Association
Authors: Bernstein Michael A.
Published: December 2008

Abstract

The 20th‐century American economics profession and its leading professional organization—the American Economic Association (AEA)—were privileged and shaped by the federal government's need to direct resources and to call on experts. Bureaucratic tendencies to classify and count had an impact on the discipline's self‐concept, the articulation of subdisciplines, and the establishment of multiple research agendas. They also powerfully framed the strategies for growth and development formulated and deployed by the AEA itself. A consensus of professional opinion and the standardization of curriculums emerged out of the involvement of economists and the AEA with governmental affairs. At the same time, such public engagement was fraught with risks and contradictions—posing challenges and difficulties with which the AEA and the profession would have to contend for decades to come.
A Prospective Observational Study of the Effect of Etomidate on Septic Patient Mortality and Length of Stay
Authors: Tekwani Karis L. , Watts Hannah F. , Rzechula Kathleen H. , Sweis Rolla T. , Kulstad Erik B.
Published: December 2008

Objectives:  Etomidate is known to cause adrenal suppression after single‐bolus administration. Some studies suggest that when etomidate is used as an induction agent for intubation of septic patients in the emergency department (ED), this adrenal suppression leads to increased mortality, vasopressor requirements, and length of hospital stay. The authors sought to determine differences in the in‐hospital mortality and hospital length of stay (LOS) between septic patients given etomidate and patients given alternative or no induction agents for rapid‐sequence intubation in our ED.

Methods:  This was a nonrandomized, prospective observational study of all patients meeting sepsis criteria who were intubated in an ED over a 9‐month period. Times of patient presentation, intubation, admission, discharge, and/or death were recorded, as well as the intubation agent used, if any, and corticosteroid use. The authors also recorded relevant laboratory and demographic variables to determine severity of illness using the Mortality in Emergency Department Sepsis (MEDS) score. Mortality and survivor LOS between the patients given etomidate and those given alternative or no induction agents were compared.

Results:  A total of 106 patients with sepsis were intubated over the study period. Of these, 74 patients received etomidate, while 32 patients received ketamine, benzodiazepines, propofol, or no induction agents. Age in years (median = 78; interquartile range [IQR] = 67 to 83), gender (45% male), MEDS score (median = 13; IQR = 10 to 15), and receipt of supplemental corticosteroids (56%) were statistically similar between the two groups. In‐hospital mortality of patients given etomidate (38%; 95% confidence interval [CI] = 28% to 49%) was similar to those receiving alternatives (44%; 95% CI = 28% to 61%). Surviving patients had a median hospital LOS after receiving etomidate of 10 days compared to those receiving alternatives (7.5 days; p = 0.08).

Conclusions:  No statistically significant increase in hospital LOS or mortality in patients given etomidate for rapid‐sequence intubation was found. Suggestions that the use of etomidate for intubation in the ED be abandoned are not supported by these data.
Alloiococcus otitidis—otitis media pathogen or normal bacterial flora?
Authors: TANO KRISTER , VON ESSEN ROBERT , ERIKSSON P.‐O. , SJÖSTEDT ANDERS
Published: December 2008

During the last decade a new potential otitis media pathogen, Alloiococcus otitidis, has been studied. It is still not clear whether this bacterium really is a pathogen, although it has been found in a high percentage of middle ear effusions in children. The present study aimed to investigate the presence of A. otitidis in the nasopharynx and outer ear canals, and to develop a culture method that would make it possible to isolate A. otitidis from these locations. Nasopharyngeal samples (n=129) from children below 6 years were investigated by conventional culture on blood agar plates with 6% saline and rabbit antisera against A. otitidis, and by a PCR method. In the same way, we investigated 10 samples from vestibulum nasi of healthy persons, 68 samples from outer ear canals of patients with acute or chronic ear problems, and 24 samples from outer ear canals of healthy persons. In a rat model of acute otitis media, we instilled living A. otitidis into rat middle ears through the tympanic bulla and evaluated the outcome clinically by otomicroscopy at days 3, 6 and 14. Of the 129 nasopharyngeal cultures, 9 were positive for A. otitidis by PCR, but none by the culture method. Of the 68 samples from patients with running ears, 4 were positive for A. otitidis by PCR, but none by the culture method. Of the 24 healthy ear canals, 7 were positive for A. otitidis by PCR and 3 of them also by the culture method. No A. otitidis could be found from the vestibulum nasi. The rat experiment showed that the reactions in the middle ears were mild; we could not provoke a purulent acute otitis media in any of the rats. There was a 7% prevalence of A. otitidis in children below 6 years. The highest prevalence (29%) was found in outer ear canals of healthy persons, which strongly suggests that A. otitidis is part of the normal bacterial flora of the outer ear canal. The doubtful pathogenicity is also confirmed by the fact that—in the rat model—A. otitidis elicited only a mild response in the middle ear. It was possible to isolate A. otitidis using a blood agar plate with 6% saline.
Dipeptidyl peptidase IV expression in cancer and stromal cells of human esophageal squamous cell carcinomas, adenocarcinomas and squamous cell carcinoma cell lines
Authors: GOSCINSKI MARIUSZ ADAM , SUO ZHEN HE , NESLAND JAHN MARTHIN , FLØRENES VIVI ANN , GIERCKSKY KARL‐ERIK
Published: December 2008

Dipeptidyl peptidase IV (DPPIV) is a transmembrane serine protease which is involved in the process of tumor invasion and development of metastases in human cancers. The aim of this study was to investigate the expression of DPPIV in cancer and stromal cells of both esophageal adenocarcinoma and squamous cell carcinoma (SCC). Tissue material from 159 patients was analyzed using immunohistochemistry. Western blotting was performed on cell lines and fresh frozen tissue sections. Results were compared with clinicopathological features. Evaluation of the immunohistochemical findings revealed significant differences between DPPIV expression in carcinoma cells and stromal cells, depending on the histological tumor type. A significantly higher level of DPPIV was found in adenocarcinomas compared to SCCs while no DPPIV was detected in normal esophageal epithelium. Overexpression of DPPIV in patients with adenocarcinoma was additionally associated with distant metastases. Thus, differences of DPPIV level in esophageal carcinomas compared with normal epithelium showed that esophageal malignancies were associated with an increased amount of cell surface‐bound DPPIV. Radiotherapy in patients had no impact on DPPIV expression in analyzed tissue samples. There was no correlation between DPPIV expression in cancer or stromal cells and survival of the patients.
A Retrospective Study on 287 Implants Installed in Resorbed Maxillae Grafted with Fresh Frozen Allogenous Bone
Authors: Carinci Francesco , Brunelli Giorgio , Franco Maurizio , Viscioni Alessandro , Rigo Leone , Guidi Riccardo , Strohmenger Laura
Published: December 2008

Background: Several studies have been performed to evaluate the clinical outcome of implants inserted into maxillae grafted with autogenous bone but few reports have focused on maxillae grafted with fresh‐frozen allogenous bone (FFAB).

Purpose: The purpose of this study is to retrospectively evaluate the clinical outcome of implants installed in resorbed maxillae augmented with FFAB.

Materials and Methods: A total of 69 patients whom had been treated with FFAB grafts to their maxillae and implant placement 4 to 6 months later were retrospectively evaluated. Edentulism was total and partial in 22 and 47 cases, respectively. A total of 287 implants of various systems had been used. A life table analysis was performed. Marginal bone loss was calculated in radiographs.

Results: Five of the 287 implants were lost, giving a survival rate (SVR) of 98.3% over a mean follow‐up time of 26 months. The marginal bone resorption at the implants was 1.68 mm (SD = 0.44) after 1 year and 1.85 mm (SD = 0.98) after 4 years. The cumulative success rate based on defined criteria was 96% in the first year but decreased to 40% at 4 years because of marginal bone loss. The Kaplan–Meier algorithm demonstrated a better outcome for female patients, removable dentures, and total edentulism. No differences were detected among diameters, lengths, and implant site.

Conclusion: Implants placed in FFAB showed a high SVR similar to that reported in previous studies on maxillae grafted with autogenous iliac crest bone. Although our data point to more marginal bone loss in partially edentulous patients and for fixed prosthetic restorations, the use of FFAB for reconstruction of the atrophic jaw prior to implant placement can be considered as a reliable alternative to autogenous bone.
Laboratory Forum: Experimental Models of Peyronie’s Disease. Implications for New Therapies
Authors: Gonzalez-Cadavid Nestor F. , Rajfer Jacob
Published: December 2008

Introduction

Despite its high prevalence and impact on the quality of life of patients, and that it is an excellent model for the study of fibrotic processes, Peyronie’s disease (PD) is an orphan disease in biomedical research. The development of animal and cell culture models has advanced substantially the understanding of its molecular and cellular pathology and the proposal of new therapies.

Aim

To review the literature pertaining to the use of these models for the study of PD.

Methods

PubMed search conducted from the first report of an animal model for PD.

Results

This model, based on the finding that transforming growth factor β1 (TGFβ1) is overexpressed in the PD plaque, consists on the injection of TGFβ1 into the tunica albuginea of the rat. This leads to a PD-like plaque retaining many of the histological and biochemical features of human PD. Another rat model, based on the hypothesis that the PD plaque arises from trauma to the penis, causing fibrinogen extravasation that initiates as fibrin a fibrotic response, consists on injection of fibrin into the tunica. The cell culture model is based on the demonstration that myofibroblasts are abundant in the human PD plaque.

Conclusions

These models have: (i) clarified the role of microtrauma, myofibroblasts, and oxidative stress in plaque development; (ii) demonstrated that this tissue is under sustained turnover by fibrotic and antifibrotic mechanisms; (iii) showed the interplay of collagenolytic and fibrinolytic systems and their inhibitors; (iv) detected an endogenous antifibrotic process consisting of the expression of inducible nitric oxide synthase that counteracts oxidative stress, collagen synthesis, and myofibroblast generation; (v) characterized the antifibrotic effects of chronic treatment with phosphodiesterase type 5 (PDE5) inhibitors; (vi) discovered the cytogenetic instability of PD cells and alterations in their gene expression; and (vii) detected stem cells in the tunica albuginea with a potential role in fibrosis and ossification.
Increased Endothelial Apoptotic Cell Density in Human Diabetic Erectile Tissue—Comparison with Clinical Data
Authors: Costa Carla , Soares Raquel , Castela Ângela , Adães Sara , Hastert Véronique , Vendeira Pedro , Virag Ronald
Published: December 2008

Introduction

Erectile dysfunction (ED) is a common complication of diabetes. Endothelial cell (EC) dysfunction is one of the main mechanisms of diabetic ED. However, loss of EC integrity has never been assessed in human diabetic corpus cavernosum.

Aim

To identify and quantify apoptotic cells in human diabetic and normal erectile tissue and to compare these results with each patient’s clinical data and erection status.

Methods

Eighteen cavernosal samples were collected, 13 from diabetics with ED and 5 from nondiabetic individuals. Cavernosal structure and cell proliferation status were evaluated by immunohistochemistry. Tissue integrity was assessed by terminal transferase dUTP nick end labeling assay, an index of apoptotic cell density (ACD) established and compared with each patient age, type of diabetes, arterial risk factors number, arterial/veno-occlusive disease, response to intracavernous vasoactive injections (ICI), and penile nitric oxide release test (PNORT).

Main Outcome Measures

Establish an index of ACD and correlate those results with patient clinical data.

Results

Nondiabetic samples presented few scattered cells in apoptosis and an ACD of 7.15 ± 0.44 (mean apoptotic cells/tissue area mm2 ± standard error). The diabetic group showed an increased ACD of 23.82 ± 1.53, and apoptotic cells were located specifically at vascular sites. Rehabilitation of these endothelial lesions seemed impaired, as no evidence of EC proliferation was observed. Furthermore, higher ACD in diabetic individuals correlated to poor response to PNORT and to ICI.

Conclusions

We provided evidence for the first time that loss of cavernosal EC integrity is a crucial event involved in diabetic ED. Furthermore, we were able to establish a threshold between ACD values and cavernosal tissue functionality, as assessed by PNORT and vasoactive ICI.
Convivencia in Medieval Spain: A Brief History of an Idea
Authors: Wolf Kenneth Baxter
Published: December 2008

Convivencia refers to the ‘coexistence’ of Christian, Muslim, and Jewish communities in medieval Spain and by extension the cultural interaction and exchange fostered by such proximity. The term first appeared as part of a controversial thesis about Spanish historical identity advanced by Américo Castro in 1948. Since then interest in the idea of convivencia has spread, fueled in part by increased attention to multi‐culturalism and rising concern about religiously framed acts of violence. The application of social scientific models has gone a long way toward clarifying the mechanisms of acculturation at work in medieval Spain and tempering the tendency to romanticize convivencia.
Oxidative stress may modify zinc protoporphyrin/heme ratio in hematofluorometry
Authors: JANOUSEK S. J. , ROSA L. , JANOUSEK S. , JIROVA D. , KEJLOVA K.
Published: December 2008

Washed red blood cells (RBCs), supplemented or non‐supplemented with sodium azide (to inhibit catalase activity), were exposed to different concentrations of hydrogen peroxide as well as ascorbic acid. Strikingly, catalase within RBCs protected the cells against exogenic hydrogen peroxide even at millimolar concentrations. However, the activity of the erythrocytic catalase failed to protect the RBCs when they were exposed to an oxidative burst of stimulated polymorphonuclear cells (PMNCs) in the presence of several reactive species in addition to peroxide. Oxyhemoglobin, with an excess of hydrogen peroxide, formed oxidized hemoglobin species and caused protein denaturation as well as the rise of heme degradation products which was suspected to falsify zinc protoporphyrin/heme (ZPP/heme) ratio as assessed by hematofluorometry. Our experiments may thus imply that the non‐fluorescent hemoglobin background can be modified by reactive oxygen species (ROS) and this can lead to a spurious ZPP/heme ratio. We discuss this phenomenon with respect to ZPP quantification in clinical practice.
Bargaining towards collusion
Authors: Rhodes Andrew
Published: December 2008

A model in which firms bargain over a collusive price is presented. The structure of an industry affects not only the ability of firms to collude, but also the collusive price itself. Entry into an industry can therefore result in consumers paying a higher price, even if the entrant is as efficient as the incumbent firms.
Why have economists done so well in the British civil service?
Authors: Allan Lewis
Published: December 2008

Economists are uniquely large in number and influence in the British civil service compared to other professionals. The significant number and influence of economists is a comparatively recent phenomenon, dating predominantly from the foundation of the Government Economic Service in 1964, with some roots in the Second World War. Reasons spanning from the role of economists as ‘arch‐rationalizers’ to the rise in influence of the Treasury are advanced to explain this development. It is noted that while economists have proliferated in Whitehall, they have yet to do so in Westminster.
Industrial Organization: The Oxford Influence (1952–1979)
Authors: Arena Lise
Published: December 2008

This article seeks to provide a better understanding of the history of Industrial Organization (IO). More precisely, it stresses the specific influence Oxford economists had between 1952 and 1979 on the developments of modern trends in the discipline. This work focuses on three main sub‐fields of IO, namely, the empirical approach to concrete forms of organization prevailing in the managerial world, the impact of information and knowledge on the discipline, and the use of game theory within IO.
Strategic judgment proofing
Authors: Che Yeon‐Koo , Spier Kathryn E.
Published: December 2008

A liquidity‐constrained entrepreneur raises capital to finance a business activity that may harm bystanders. The entrepreneur raises senior (secured) debt to shield assets from the tort victims in bankruptcy. For a fixed level of borrowing, senior debt creates better incentives for precaution taking than either junior debt or outside equity. The entrepreneur's level of borrowing is, however, socially excessive. Giving tort victims priority over senior debtholders in bankruptcy prevents overleveraging but leads to suboptimal incentives. Lender liability exacerbates the incentive problem even further. A limited seniority rule dominates these alternatives. Shareholder liability, mandatory liability insurance, and punitive damages are also discussed.
Emodin reverses CCl4induced hepatic cytochrome P450 (CYP) enzymatic and ultrastructural changes: Thein vivoevidence
Authors: Bhadauria Monika , Nirala Satendra Kumar , Shrivastava Sadhana , Sharma Abhilasha , Johri Sonia , Chandan Bal Krishan , Singh Bhupendar , Saxena Ajit Kumar , Shukla Sangeeta
Published: December 2008

Aim: The curative effect of emodin (1,3,8‐trihydroxy‐6‐methyl anthraquinone), an active compound of the plant speciesVentilago maderaspatanaGaertn, was evaluated against carbon tetrachloride (CCl4) induced hepatic cytochrome P450 (CYP) enzymatic and ultrastructural alterations in rats.

Methods: Female rats were administered CCl4(1.5 mL/kg, ip) followed by varying doses of emodin (20, 30 and 40 mg/kg, oral po) after 24 h of CCl4administration. Animals were euthanized after 24 h of last administration to determine liver function tests in serum, hepatic light microscopic and ultrastructural changes, activity of CYP enzymes, microsomal lipid peroxidation and protein contents, hexobarbitone induced sleep time and bromosulphalein retention.

Results: The CCl4induced‐toxic effects were observed with sharp elevation in the release of serum transaminases, alkaline phosphatase, lactate dehydrogenase and γ‐glutamyl transpeptidase. An initial study for an optimum dose of emodin among different dose levels revealed that a 30 mg/kg dose was effective in restoring all the enzymatic variables and liver histoarchitecture in a dose dependent manner. Exposure to CCl4diminished the activities of CYP enzymes (i.e. aniline hydroxylase and amidopyrine‐N‐demethylase and microsomal protein contents with concomitant increase in microsomal lipid peroxidation). Emodin at 30 mg/kg effectively reversed the CCl4induced hepatotoxic events, which was consistent with ultrastructural observations. Hexobarbitone‐induced sleep time and plasma bromosulphalein retention also improved liver functions after emodin therapy.

Conclusion: By reversal CYP activity and ultrastructural changes, emodin shows a strong hepatoprotective abilities.
Friction Measurement in the Biaxial Rocking Motion Hip Joint Simulator
Authors: Saikko Vesa
Published: December 2008

The established biaxial rocking motion (BRM) hip joint simulator was complemented by a novel friction measurement accessory. This simple and practical system, which was easily added to an existing BRM design, is described in detail and shown to perform well in long-term wear tests and in comparative tests of 24 h duration involving several different bearing couples. The system was based on the measurement of frictional torque about the leaning axis of the lower component, the femoral head. In the 28 mm CoCr-on-ultrahigh molecular weight polyethylene articulation with diluted calf serum lubricant at body temperature and 1 kN static load, the maximum value of frictional torque during a cycle was 1.2 N m on the average. The alternative system based on the measurement of torque about the vertical loading axis was shown to be less sensitive and highly insensitive when contact area was small, as was the case with alumina-on-alumina.
Elastic-Plastic Wheel-Rail Thermal Contact on Corrugated Rails During Wheel Braking
Authors: Chen Yung-Chuan , Lee Sing-You
Published: December 2008

This study uses an elastic-plastic, coupled temperature-displacement finite element model to investigate the effect of rail corrugations on the wheel-rail thermal contact stress and temperature distribution during wheel braking. The finite element model assumes that the material properties and the friction coefficient are temperature-dependent. The analysis considers various corrugation wavelengths and amplitudes and is performed over a range of braking speeds. The results indicate that the corrugated rail induces wavelike contact pressure and temperature distributions on the rail surface. The results also show that the variation in the peak contact pressure increases as the corrugation wavelength is reduced or as the corrugation amplitude is increased. Furthermore, it is found that the corrugated rail shifts the location of the peak value of the rail surface temperature toward the leading edge of the contact region. The amplitude of the temperature fluctuations reduces as the corrugation wavelength is increased or as the corrugation amplitude is reduced. Finally, a higher corrugation amplitude or a shorter corrugation wavelength causes the location of the peak maximum shear stress to shift toward the rail surface.
Analytical and Experimental Elastic-Plastic Impact Analysis of a Magnetic Storage Head-Disk Interface
Authors: Katta Raja R. , Polycarpou Andreas A. , Hanchi Jorge V. , Roy Mallika
Published: December 2008

As the use of hard disk drives in mobile applications increases, the susceptibility of disk damage due to high velocity slider-disk impact presents a serious challenge. The impact could result in extremely high contact stresses, leading to the failure of the head-disk interface. An elastic-plastic contact-mechanics-based impact model was developed and implemented to study the impact between a slider corner and a disk. The impact model is based on the contact of a rigid sphere on a deformable half-space. The effect of slider corner radii and impact velocities on the contact parameters was initially investigated for a homogeneous disk substrate. To examine the effects of thin-film layers on the disk, the model was extended to a realistic layered disk, where the actual layered mechanical properties were directly measured. At high impact velocities and/or small slider corner radii, the impact was found to be dominated by the substrate and the effect of layers was negligible. At low impact velocities and/or large slider corner radii, the effect of nanometer thick layers could be clearly seen, as these layers are stiffer than the substrate protecting the disk from potential damage at lighter loads. Realistic dynamic impact experiments involving a slider and a spinning thin-film disk were performed using an operational shock tester. The impact damage was characterized in terms of residual penetration depth caused by the impact force of the shock and the impact velocity of the slider. However, the results were inconclusive in correlating with the impact model. To better control the experimental parameters, quasistatic nanoindentation experiments were performed on actual thin-film media and were successfully compared with the model predictions.
A Particle-Augmented Mixed Lubrication Modeling Approach to Predicting Chemical Mechanical Polishing
Authors: Terrell Elon J. , Higgs C. Fred
Published: December 2008

Chemical mechanical polishing (CMP) is a manufacturing process that is commonly used to planarize integrated circuits and other small-scale devices during fabrication. Although a number of models have been formulated, which focus on specific aspects of the CMP process, these models typically do not integrate all of the predominant mechanical aspects of CMP into a single framework. Additionally, the use of empirical fitting parameters decreases the generality of existing predictive CMP models. Therefore, the focus of this study is to develop an integrated computational modeling approach that incorporates the key physics behind CMP without using empirical fitting parameters. CMP consists of the interplay of four key tribological phenomena—fluid mechanics, particle dynamics, contact mechanics, and resulting wear. When these physical phenomena are all actively engaged in a sliding contact, the authors call this particle-augmented mixed lubrication (PAML). By considering all of the PAML phenomena in modeling particle-induced wear (or material removal), this model was able to predict wear-in silico from a measured surface topography during CMP. The predicted material removal rate (MRR) was compared with experimental measurements of copper CMP. A series of parametric studies were also conducted in order to predict the effects of varying slurry properties such as solid fraction and abrasive particle size. The results from the model are promising and suggest that a tribological framework is in place for developing a generalized first-principle PAML modeling approach for predicting CMP.
Analysis on Dynamic Performance of Hydrodynamic Tilting-Pad Gas Bearings Using Partial Derivative Method
Authors: Lihua Yang , Shemiao Qi , Lie Yu
Published: December 2008

Tilting-pad gas bearings are widely used in high-speed rotating machines due to their inherent stability characteristics. This paper advances the analytical method for prediction of the dynamic performances of tilting-pad gas bearings. The main advantage of the analytical method is that the complete set of dynamic coefficients of tilting-pad gas bearings can be obtained. The predictions show that the perturbation frequency has the strong effects on the dynamic coefficients of gas bearings. In general, at lower perturbation frequency, the equivalent direct stiffness coefficients increase with frequency, whereas equivalent direct damping coefficients dramatically reduce. For higher perturbation frequency, the dynamic coefficients are nearly independent of the frequency. Moreover, the equivalent dynamic coefficients of four-pad tilting-pad gas bearing obtained by the method in this paper are in good agreement with those obtained by Zhu and San Andres [(2007), “Rotordynamic Performance of Flexure Pivot Hydrostatic Gas Bearings for Oil-Free Turbomachinery,” ASME J. Eng. Gas Turbines Power, 129(4), pp. 1020–1027] in the published paper. The results validate the feasibility of the method presented in this paper in calculating the dynamic coefficients of gas-lubricated tilting-pad bearings.
Measurement and Sources of Lateral Tape Motion: A Review
Authors: Raeymaekers Bart , Talke Frank E.
Published: December 2008

The sources of lateral tape motion in a tape drive are reviewed. Currently used measurement methods and models for lateral tape motion are analyzed and compared. The effect of roller run-out, tape edge contact, and tape tension transients on lateral tape motion is discussed. A dual stage actuator tape head is investigated to improve track-following capability and increase the track density on a magnetic tape.
Image artifacts in digital breast tomosynthesis: Investigation of the effects of system geometry and reconstruction parameters using a linear system approach
Authors: Hu Yue‐Houng , Zhao Bo , Zhao Wei
Published: December 2008

Digital breast tomosynthesis (DBT) is a three‐dimensional (3D) x‐ray imaging modality that reconstructs image slices parallel to the detector plane. Image acquisition is performed using a limited angular range (less than ) and a limited number of projection views (less than 50 views). Due to incomplete data sampling, image artifacts are unavoidable in DBT. In this preliminary study, the image artifacts in DBT were investigated systematically using a linear system approximation. A cascaded linear system model of DBT was developed to calculate the 3D presampling modulation transfer function (MTF) with different image acquisition geometries and reconstruction filters using a filtered backprojection (FBP) algorithm. A thin, slanted tungsten (W) wire was used to measure the presampling MTF of the DBT system in the cross‐sectional plane defined by the thickness and tube travel directions. The measurement was in excellent agreement with the calculation using the model. A small steel bead was used to calculate the artifact spread function (ASF) of the DBT system. The ASF was correlated with the convolution of the two‐dimensional (2D) point spread function (PSF) of the system and the object function of the bead. The results showed that the cascaded linear system model can be used to predict the magnitude of image artifacts of small, high‐contrast objects with different image acquisition geometry and reconstruction filters.
In vivo quantification of contrast agent concentration using the induced magnetic field for time‐resolved arterial input function measurement with MRI
Authors: de Rochefort Ludovic , Nguyen Thanh , Brown Ryan , Spincemaille Pascal , Choi Grace , Weinsaft Jonathan , Prince Martin R. , Wang Yi
Published: December 2008

For pharmacokinetic modeling of tissue physiology, there is great interest in measuring the arterial input function (AIF) from dynamic contrast‐enhanced (DCE) magnetic resonance imaging (MRI) using paramagnetic contrast agents. Due to relaxation effects, the measured signal is a nonlinear function of the injected contrast agent concentration and depends on sequence parameters, system calibration, and time‐of‐flight effects, making it difficult to accurately measure the AIF during the first pass. Paramagnetic contrast agents also affect susceptibility and modify the magnetic field in proportion to their concentration. This information is contained in the MR signal phase which is discarded in a typical image reconstruction. However, quantifying AIF through contrast agent susceptibility induced phase changes is made difficult by the fact that the induced magnetic field is nonlocal and depends upon the contrast agent spatial distribution and thus on organ and vessel shapes. In this article, the contrast agent susceptibility was quantified through inversion of magnetic field shifts using a piece‐wise constant model. Its feasibility is demonstrated by a determination of the AIF from the susceptibility‐induced field changes of an intravenous bolus. After in vitro validation, a time‐resolved two‐dimensional (2D) gradient echo scan, triggered to diastole, was performed in vivo on the aortic arch during a bolus injection of Gd‐DTPA. An approximate geometrical model of the aortic arch constructed from the magnitude images was used to calculate the spatial variation of the field associated with the bolus. In 14 subjects, Gd concentration curves were measured dynamically (one measurement per heart beat) and indirectly validated by independent 2D cine phase contrast flow rate measurements. Flow rate measurements using indicator conservation with this novel quantitative susceptibility imaging technique were found to be in good agreement with those obtained from the cine phase contrast measurements in all subjects. Contrary to techniques that rely on intensity, the accuracy of this signal phase based method is insensitive to factors influencing signal intensity such as flip angle, coil sensitivity, relaxation changes, and time‐of‐flight effects extending the range of pulse sequences and contrast doses for which quantitative DCE‐MRI can be applied.
Automated regional registration and characterization of corresponding microcalcification clusters on temporal pairs of mammograms for interval change analysis
Authors: Filev Peter , Hadjiiski Lubomir , Chan Heang‐Ping , Sahiner Berkman , Ge Jun , Helvie Mark A. , Roubidoux Marilyn , Zhou Chuan
Published: December 2008

A computerized regional registration and characterization system for analysis of microcalcification clusters on serial mammograms is being developed in our laboratory. The system consists of two stages. In the first stage, based on the location of a detected cluster on the current mammogram, a regional registration procedure identifies the local area on the prior that may contain the corresponding cluster. A search program is used to detect cluster candidates within the local area. The detected cluster on the current image is then paired with the cluster candidates on the prior image to form true (TP‐TP) or false (TP‐FP) pairs. Automatically extracted features were used in a newly designed correspondence classifier to reduce the number of false pairs. In the second stage, a temporal classifier, based on both current and prior information, is used if a cluster has been detected on the prior image, and a current classifier, based on current information alone, is used if no prior cluster has been detected. The data set used in this study consisted of 261 serial pairs containing biopsy‐proven calcification clusters. An MQSA radiologist identified the corresponding clusters on the mammograms. On the priors, the radiologist rated the subtlety of 30 clusters (out of the 261 clusters) as 9 or 10 on a scale of 1 (very obvious) to 10 (very subtle). Leave‐one‐case‐out resampling was used for feature selection and classification in both the correspondence and malignant/benign classification schemes. The search program detected 91.2% of the clusters on the priors with an average of 0.42 FPs/image. The correspondence classifier identified 86.6% of the TP‐TP pairs with 20 false matches (0.08 FPs/image) relative to the entire set of 261 image pairs. In the malignant/benign classification stage the temporal classifier achieved a test of 0.81 for the 246 pairs which contained a detection on the prior. In addition, a classifier was designed by using the clusters on the current mammograms only. It achieved a test of 0.72 in classifying the clusters as malignant and benign. The difference between the performance of the temporal classifier and the current classifier was statistically significant . Our interval change analysis system can detect the corresponding cluster on the prior mammogram with high sensitivity, and classify them with a satisfactory accuracy.
Lung tumor tracking in fluoroscopic video based on optical flow
Authors: Xu Qianyi , Hamilton Russell J. , Schowengerdt Robert A. , Alexander Brian , Jiang Steve B.
Published: December 2008

Respiratory gating and tumor tracking for dynamic multileaf collimator delivery require accurate and real‐time localization of the lung tumor position during treatment. Deriving tumor position from external surrogates such as abdominal surface motion may have large uncertainties due to the intra‐ and interfraction variations of the correlation between the external surrogates and internal tumor motion. Implanted fiducial markers can be used to track tumors fluoroscopically in real time with sufficient accuracy. However, it may not be a practical procedure when implanting fiducials bronchoscopically. In this work, a method is presented to track the lung tumor mass or relevant anatomic features projected in fluoroscopic images without implanted fiducial markers based on an optical flow algorithm. The algorithm generates the centroid position of the tracked target and ignores shape changes of the tumor mass shadow. The tracking starts with a segmented tumor projection in an initial image frame. Then, the optical flow between this and all incoming frames acquired during treatment delivery is computed as initial estimations of tumor centroid displacements. The tumor contour in the initial frame is transferred to the incoming frames based on the average of the motion vectors, and its positions in the incoming frames are determined by fine‐tuning the contour positions using a template matching algorithm with a small search range. The tracking results were validated by comparing with clinician determined contours on each frame. The position difference in 95% of the frames was found to be less than in the best case and in the worst case for the five patients studied.
Model for the detection of signals in images with multiple suspicious locations
Authors: Popescu Lucreţiu M.
Published: December 2008

A signal detection model is presented that combines a signal model and a noise model providing mathematical descriptions of the frequency of appearance of the signals, and of the signal‐like features naturally occurring in the background. We derive expressions for the likelihood functions for the whole ensemble of observed suspicious locations, in various possible combinations of signals and false signal candidates. As a result, this formalism is able to describe several new types of detection tests using likelihood ratio statistics. We have a global image abnormality test and an individual signal detection test. The model also provides an alternative mechanism in which is selected the combination of signal and noise features candidates that has the maximum likelihood. These tests can be analyzed with a variety of operating characteristic curves (ROC, LROC, FROC, etc.). In the mathematical formalism of the model, all the details characterizing the suspicious features are reduced to a single scalar function, which we name the signal specificity function, representing the frequency that a signal takes a certain value relative to the frequency of having a false signal with the same value in an image of given size. The signal specificity function ranks the degree of suspiciousness of the features found, and can be used to unify into a single score all the suspicious feature characteristics, and then apply the usual decision conventions as in the Swensson's detection model [Med. Phys. 23, 1709–1725 (1996)]. We present several examples in which these tests are compared. We also show how the signal specificity function can be used to model various degrees of accuracy of the observer's knowledge about image noise and signal statistical properties. Aspects concerning modeling of the human observer are also discussed.
Pulmonary CT image registration and warping for tracking tissue deformation during the respiratory cycle through 3D consistent image registration
Authors: Li Baojun , Christensen Gary E. , Hoffman Eric A. , McLennan Geoffrey , Reinhardt Joseph M.
Published: December 2008

Tracking lung tissues during the respiratory cycle has been a challenging task for diagnostic CT and CT‐guided radiotherapy. We propose an intensity‐ and landmark‐based image registration algorithm to perform image registration and warping of 3D pulmonary CT image data sets, based on consistency constraints and matching corresponding airway branchpoints. In this paper, we demonstrate the effectivenss and accuracy of this algorithm in tracking lung tissues by both animal and human data sets. In the animal study, the result showed a tracking accuracy of between 50% functional residual capacity (FRC) and 85% total lung capacity (TLC) for 12 metal seeds implanted in the lungs of a breathing sheep under precise volume control using a pulmonary ventilator. Visual inspection of the human subject results revealed the algorithm's potential not only in matching the global shapes, but also in registering the internal structures (e.g., oblique lobe fissures, pulmonary artery branches, etc.). These results suggest that our algorithm has significant potential for warping and tracking lung tissue deformation with applications in diagnostic CT, CT‐guided radiotherapy treatment planning, and therapeutic effect evaluation.