bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevention of Diet–Induced Fatty Liver in Experimental Animals by the Oral Administration of A Fatty Acid Bile Acid Conjugate (Fabac)
Authors: Gilat Tuvia , Leikin-Frenkel Alicia , Goldiner Ilana , Juhel Christine , Lafont Huguette , Gobbi Diana , Konikoff Fred M.
Published: July 2003

Fatty acid bile acid conjugates (FABACs) are a new family of synthetic molecules designed to solubilize biliary cholesterol. They were shown to prevent and dissolve cholesterol gallstones in inbred C57L/J mice fed a lithogenic, high–fat diet (HFD). In these mice, fatty liver was observed in the controls but not in the FABAC–treated ones. The present study was designed to study the effect of FABAC (arachidyl–amido–cholanoic acid) on diet–induced fatty liver in rats, hamsters, and mice. The fatty liver score (on a scale of 0–4 by light microscopy) was 4.0 in control hamsters and 0.3 in the FABAC–fed hamsters (P < .001). In mice it was 1.5 and 0.4, respectively (P < .01). The lipid/protein ratio in the liver was 1.3 ± 0.44 (mg lipid/mg protein) in control rats and 0.66 ± 0.04 in the FABAC group (P = .001) after 14 days. In hamsters it was 1.41 ± 0.27 and 1.11 ± 0.20, respectively (P = .03), after 21 days. In Imperial Charles River (ICR) mice the ratio was 0.34 ± 0.10 and 0.17 ± 0.07 (P = .03), respectively, after 24 days. Liver fat concentration, measured as mg lipid/g liver tissue, decreased similarly by FABAC feeding. The decrease in liver fat affected mainly the triglyceride levels. FABAC–fed animals gained weight similarly to the controls. Triglyceride absorption was unaffected by FABAC supplementation. In conclusion, oral FABAC therapy prevents/reduces the development of fatty liver in animals consuming a HFD.
Liver transplantation in neonates
Authors: Sundaram Shikha S. , Alonso Estella M. , Whitington Peter F.
Published: July 2003

Orthotopic liver transplantation (OLT) has evolved over the past two decades to become the standard of care for end-stage liver disease in infants and children. Technical advances, particularly the use of technical variant allografts, have permitted extension of OLT into a much younger and smaller population than previously possible. Major centers around the world now routinely perform OLT in infants with survival success equivalent to that in older children and adults. We are beginning to see a small population of school-aged children who were infant OLT recipients. The further extension of OLT into neonates is more recent, with only a few pediatric centers reporting survival success. Very little is known about this frontier of transplantation. Our intent is to provide an overview of neonatal OLT using all available data and our experience in the field
Safety and outcome of hepatitis B core antibody-positive donors in right-lobe living donor liver transplantation
Authors: Lo Chung-Mau , Fan Sheung-Tat , Liu Chi-Leung , Yong Boon-Hun , Wong Yik , Ng Irene Oi-Lin , Wong John
Published: July 2003

We studied the safety of right-lobe donor hepatectomy in living donors with a positive serological test result for antibody against hepatitis B core antigen (anti-HBc). Of 54 right-lobe living liver donors, serum anti-HBc was positive in 29 donors (54%) and negative in 25 donors (46%). None had a history of hepatitis and all had normal liver biochemistry test results before surgery. Surgical data, postoperative liver function, and outcome of donors were compared according to anti-HBc status. Donors positive for anti-HBc were significantly older (median age, 42 v 31 years; P < .001), but there was no difference in other demographics and liver size. Median blood loss was greater in anti-HBc-positive donors (600 v 350 mL; P = .007). Histological examination showed no difference in degree of portal fibrosis or fatty change in liver grafts. There was no significant difference in postoperative serum transaminase levels or prothrombin times; however, anti-HBc-positive donors had greater serum bilirubin levels day 6 (26 v 21 μmol/L; P = .01) and day 7 (22 v 15 μmol/L; P = .004) after surgery. Postoperative complications developed in 10 anti-HBc-positive and 6 anti-HBc-negative donors (P = .4). All donors who developed cholestasis were positive for anti-HBc, aged 45 years or older, and had mild fatty changes of the liver. Hospital stays were similar. All donors had completely normal liver function at a median follow-up of 31 months (range, 21 to 76 months). A positive serological test result for anti-HBc should not be regarded as a contraindication for right-lobe liver donation. (Liver Transpl 2003;9:827-832.)
Incidence and prevalence of coccidioidomycosis in patients with end-stage liver disease
Authors: Blair Janis E. , Balan Vijayan , Douglas David D. , Hentz Joseph G.
Published: July 2003

Coccidioidomycosis is an endemic fungal infection of the desert southwestern United States. Patients with end-stage liver disease (ESLD) have not been described as having a high rate of coccidioidal infection. We prospectively evaluated 290 patients with ESLD for liver transplantation and found that 6 of these patients )2.1%) had active coccidioidal infection at presentation. Of 184 patients listed for transplantation, 48 patients were observed for at least 1 year; among these 48 patients, new coccidioidal infection developed in 2 patients within the year, for a 1-year incidence of 4.2%. Conversely, the incidence of coccidioidal infection in Maricopa County, Arizona in that same period was 0.04%. Awareness is needed to identify the presence of coccidioidal infection, which may be masked by symptoms and findings of ESLD. Treatment may alleviate some of the symptoms of coccidioidomycosis originally attributed to the concomitant liver disease
Serial measurements of bone density at the lumbar spine do not predict fracture risk after liver transplantation
Authors: Hardinger Karen L. , Ho Bing , Schnitzler Mark A. , Desai Niraj , Lowell Jeffrey , Shenoy Surendra , Chapman William , Crippin Jeffrey S.
Published: July 2003

Bone disease has emerged as a serious and complex complication after liver transplantation. The purpose of this study is to determine risk factors for fracture and bone loss after liver transplantation. Dual-energy x-ray absorptiometry (DEXA) of the lumbar spine was performed routinely pretransplantation, 6 months posttransplantation, and at yearly intervals thereafter at our center. We followed up patients who underwent transplantation in the past 10 years and compared bone mineral density (BMD) and fracture rate with known risk factors for bone loss in primary transplant recipients who met the inclusion criteria of a pretransplantation DEXA and at least one follow-up DEXA scan postoperatively (n = 153). We observed a 15% (n = 23) prevalence of symptomatic fractures at a mean of 2.2 ± 1.8 years after transplantation. Change in BMD was greatest from pretransplantation to 6 months posttransplantation (−4.2%; P = .006), then increased at a rate of 1.4% per year. Logistic regression analysis showed an association of fracture risk with several factors, including number of acute rejection episodes (P = .045), smoking (P = .02), and female sex (P = .02). Stepwise logistic regression analysis reported female sex (P = .004) as the only factor associated with fracture after transplantation. Age, time listed for transplantation, race, menopause, chronic renal insufficiency, loss of height, family history of osteoporosis, BMD, and T score did not predict fracture or bone loss after transplantation. In conclusion, serial measurements of BMD at the lumbar spine do not appear to predict fracture risk; however, data suggest that female sex is the strongest predictor of fracture after liver transplantation. (Liver Transpl 2003;9:857-862.)
Recurrent deep-vein thrombosis based on homozygous factor V Leiden mutation acquired after liver transplantation
Authors: Willems Marc , Sterneck Martina , Langer Florian , Jung Roman , Haddad Munif , Hagel Christian , Kuetemeier Robert , Eifrig Barbara , Broering Dieter , Fischer Lutz , Rogiers Xavier
Published: July 2003

Several genetic liver diseases can be treated by liver transplantation (LT). However, some genetic defects also may be acquired by this procedure. We describe a patient who developed recurrent deep-vein thromboses after LT for hepatitis C virus-associated hepatocellular carcinoma on the basis of a homozygous Leiden mutation of the factor V gene in the donor liver. Liver donors with a history of venous thrombosis should be screened for the presence of activated protein C (APC) resistance. In addition, we recommend looking for APC resistance in liver recipients who develop venous thromboembolic disease in the post-LT course. Molecular analysis of donor tissue may be necessary to make a definite diagnosis of factor V Leiden mutation in these patients. As a consequence, intensified postoperative thromboprophylaxis or lifelong anticoagulant therapy may be necessary if this thrombophilic gene defect is detected. (Liver Transpl 2003;9:870-873.)
Prolonged survival of rat liver allograft with adenoviral gene transfection of human immunodeficiency virus type 1 nef
Authors: Fujino Masayuki , Adachi Kensuke , Kawasaki Mikiko , Kitazawa Yusuke , Funeshima Naoko , Okuyama Torayuki , Kimura Hiromitsu , Li Xiao-Kang
Published: July 2003

HIV-1 nef is believed to allow immune evasion by modifying cell surface molecules because of certain mechanisms such as downregulation of the major histocompatibility complex (MHC) class I molecule complex as well as upregulation of FasL. In the present study, we successfully generated a recombinant adenovirus vector containing HIV-1 nef. We detected the expression of nef in liver infected with AxCANef by immune staining and Western blotting, and confirmed its expression as persistent for more than 4 weeks. Furthermore, the surface expression of MHC class I was downregulated in AxCANef-infected hepatic cells. In addition, we also observed nef-induced FasL upregulation of gene-transfected hepatic cells. Using a DA-to-Lewis orthotopic liver transplantation model, we transfected AxCANef to a liver graft to determine whether nef expression could have an effect on recipient survival. AxCANef significantly prolonged recipient survival time (14.5 days) compared with the uninfected group (11 days) (P < .001) and the AxCALacZ-infected group (11 days) (P < .001). Histologic analysis showed reduction in the number of accumulated inflammatory cells and an increase in apoptotic cells in grafts expressing nef. In conclusion, we showed that the nef gene could prolong survival of rat liver allografts, and this result suggested the potential clinical use of its transfection.
Cavoportal transposition for portal vein thrombosis in a pediatric living-related liver transplantation
Authors: Kumar Nagappan , Atkison Paul , Fortier Marielle V. , Grant David R. , Wall William J.
Published: July 2003

We report a case of a living-related liver transplantation in a child in whom diffuse thrombosis of the portal venous system required the use of recipient vena cava to perfuse the donor portal vein (cavoportal transposition). An 8 ½-month-old infant with biliary atresia received the left lateral segment of his father’s liver. The child’s portal vein was irretrievably thrombosed, as were the splenic and superior mesenteric veins. A cavoportal anastomosis provided excellent flow to the liver, and there was no engorgement of the graft, which had good immediate function. The main postoperative problem was loss of 3 to 3.5 liters of ascitic fluid through the drain for 2 weeks. The ascites eventually resolved over a period of 4 weeks. Twenty-four months after transplantation, the child is thriving on a normal diet and has no ascites. A Doppler examination showed good flow in the cavoportal anastomosis.
Dual-echo, chemical shift gradient-echo magnetic resonance imaging to quantify hepatic steatosis: Implications for living liver donation
Authors: Rinella Mary E. , McCarthy Richard , Thakrar Kiran , Finn John Paul , Rao Sambasiva M. , Koffron Alan J. , Abecassis Michael , Blei Andres T.
Published: July 2003

In living liver donation, a fatty liver poses risks for both recipient and donor. Currently, liver biopsy is the standard for assessing the presence and extent of steatosis. The goals of this study were to correlate a steatosis index derived from magnetic resonance imaging (MRI) to the histologic grade on biopsy as well as to determine the topographic distribution of steatosis within the liver. We examined the ability of dual-echo, chemical shift gradient-echo MRI to predict the degree of steatosis on liver biopsy. A total of 22 subjects received both a liver biopsy and detailed MRI evaluation. These individuals included 15 potential living donors and 7 patients with nonalcoholic fatty liver disease. MRI steatosis index was then compared with histologic grade on liver biopsy. The topographic distribution of hepatic steatosis was determined from those subjects in whom MRI detected hepatic steatosis. The steatosis index had a positive correlation with grade of steatosis on liver biopsy (correlation coefficient, 0.84). There was no significant variation in the degree of steatosis among segments. A steatosis index of >0.2 had good positive and negative predictive value for the presence of significant steatosis (>15%) on biopsy. Our quantitative MRI protocol can predict the degree of hepatic steatosis when it is minimal to moderate, and may obviate the need for liver biopsy for the purpose of quantification of steatosis in living donors. Fat saturation added to the MRI protocol may further improve diagnostic accuracy. This technique may be applicable to the larger population with hepatic steatosis. (Liver Transpl 2003;9:851-856.)
Setting organ allocation priorities: Should we care what the public cares about?
Authors: Johri Mira , Ubel Peter A.
Published: July 2003

Abstract

Objective:

To investigate the nature of public preferences in the allocation of donor liver grafts for transplantation.

Design:

A qualitative study based upon the transcripts of four focus groups.

Setting:

Derby, Derbyshire, UK.

Participants:

Twenty-two members of the public in the Derby locality, recruited to one of four focus groups through local community groups.

Main Outcome Measures:

The views of focus group members as to the importance (or otherwise) of several potential discriminating factors which could be used in the prioritization of patients on the waiting list for liver transplantation were ascertained. The factors included were expected posttransplantation prognosis, the age of the patient, whether the patient was personally responsible for their illness, the time spent on the waiting list, re-transplantation or primary transplant and the social background of the patient.

Results and Conclusions:

Group members explored the criteria from a number of perspectives, and made some unexpected linkages between the criteria and wider moral principles. They did not come to firm conclusions about the relative desirability of the criteria, but their approach was notably flexible and thoughtful, with the exception of a few instances where they appeared to resort to arguments based on what is ‘obvious’ and ‘natural’. The results of these discussions suggest that members of the public would be able and willing to respond positively to a more open and consultative system of donor liver prioritization than exists presently within the UK.
Multivisceral and isolated intestinal procurement techniques
Authors: Yersiz Hasan , Renz John F. , Hisatake Garrett M. , Gordon Sherylin , Saggi Bob H. , Feduska Nicholas J. , Busuttil Ronald W. , Farmer Douglas G.
Published: July 2003

Improved outcomes in multivisceral and isolated intestinal transplantation have generated increased demand for these procedures. Enhanced recognition of potential multivisceral/intestinal donors and widespread application of advanced organ procurement techniques is necessary in the current climate of organ scarcity. This manuscript details the multivisceral and isolated intestinal procurement techniques currently performed at the University of California Los Angeles.
Use of hepatitis B core antibody-positive donors in recipients without evidence of hepatitis B infection: A survey of current practice in the United States
Authors: Burton James R. , Shaw-Stiffel Thomas A.
Published: July 2003

Because of the current organ shortage, some liver transplant programs have begun to accept marginal organs that previously would have been rejected. An example is the use of donors with evidence of past hepatitis B virus (HBV) infection. To gain insight into the use of hepatitis B core antibody-positive (anti-HBc+) donor livers in recipients without evidence of HBV infection, we conducted a survey. Surveys consisting of 12 multiple-choice questions were sent to all 110 liver transplant programs across the United States in mid-2001, and 56 of 110 surveys (51%) could be evaluated. Overall, 32 of 56 programs (57%) indicated they would transplant an anti-HBc+ liver into a recipient without serological evidence of HBV infection. Of those who would accept an anti-HBc+ liver, 16 of 27 respondents (59%) indicated knowledge of HBV DNA status would change their protocol; 46% of these respondents would decrease prophylaxis if HBV DNA was negative, 27% would increase prophylaxis if HBV DNA was positive, and 27% would not accept the liver if HBV DNA was positive. Conversely, 9 of 28 respondents (32%) who would not accept an anti-HBc+ liver stated that knowing HBV DNA status would change their protocol in that they might consider accepting livers if HBV DNA was negative. In conclusion, as of mid-2001, of transplant medical directors in the United States who responded to our survey, 57% would accept an anti-HBc+ donor liver for an HBV-naïve recipient. Treatment protocols for using these organs varied. Knowledge about HBV DNA status of the donor and/or liver would greatly influence prophylaxis for those accepting anti-HBc+ donor livers.
A multicenter pilot prospective study comparing Celsior and University of Wisconsin preserving solutions for use in liver transplantation
Authors: Cavallari Antonino , Cillo Umberto , Nardo Bruno , Filipponi Franco , Gringeri Enrico , Montalti Roberto , Vistoli Fabio , D’Amico Francesco , Faenza Antonio , Mosca Franco , Vitale Alessandro , D’Amico Davide
Published: July 2003

Primary dysfunction (PDF) still occurs after orthotopic liver transplantation (OLT). Celsior solution (CS) might offer some advantages over the conventional University of Wisconsin (UW) solution for organ preservation, but to date, this has not been prospectively evaluated in the context of OLT. In this prospective, randomized, multicenter, pilot study, 215 potential liver donors were enrolled and randomized. In 42 cases, the livers were unsuitable for transplantation; therefore, 173 randomized livers ultimately were implanted after perfusion and cold preservation with CS (n = 83) or UW solution (n = 90). In accord with the indications of the CS manufacturing company, total CS infusion volume was 90 mL/kg, greater than that of UW solution (60 mL/kg). The main aim of the study is to compare the prevalence of PDF between the two groups. Donor and recipient variables were similar in the two groups. Episodes of PDF were numerically lower in the CS (2.4%) than UW group (7.8%), but the difference was not statistically significant. There was a trend toward a lesser need for early re-OLT (<30 days) in the CS group (P = .0507), but again, no statistically significant difference emerged. Overall and time-differentiated postoperative deaths also were similar. One-year actuarial patient (UW, 89% v CS, 87%) and graft (UW, 83% v CS, 85%) survival rates were similar. In conclusion, CS was similar to UW solution as a preservation solution in the clinical setting of OLT at the infusion volumes described, although some theoretical advantages of CS composition suggest that CS might prove a valid alternative to UW preservation solution in multiorgan harvesting, including the liver. A study on a larger patient basis is needed.
Impact of right-lobe live donor liver transplantation on patients waiting for liver transplantation
Authors: Liu Chi-Leung , Lam Banny , Lo Chung-Mau , Fan Sheung-Tat
Published: July 2003

Right-lobe live donor liver transplantation (LDLT) is accepted for adult patients, but the incremental benefit of LDLT over cadaveric donor liver transplantation (CDLT) is unknown. We evaluated prospectively the impact of right-lobe LDLT on patients listed for CDLT. Between January 1999 and December 2001, a total of 152 patients with chronic liver disease were listed for liver transplantation. The options of LDLT and CDLT were given after listing. Sixty-five patients (43%) had volunteers and 87 patients (57%) did not have volunteers. The groups with and without volunteers were similar in terms of age, diagnosis of liver disease, and Model for End-Stage Liver Disease score. The group with volunteers had a shorter waiting time for transplantation (median, 38 v 344 days; P < .001), greater transplantation rate (72% v 20%; P < .001), and lower mortality rate while waiting for a transplant (15% v 30%; P = .037). Overall, right-lobe LDLT was performed in 44 patients (29%). It increased the transplantation rate from 13% to 42%. On follow-up until December 2002 (median follow-up, 17.4 months), survival rates of the groups with and without volunteers were 68% and 51%, respectively (P = .034). One- and 3-year survival rates were 72.3% and 66.4% for the group with volunteers and 61.9% and 45.6% for the group without volunteers, respectively (P = .028). In conclusion, right-lobe LDLT offers patients listed for transplantation an incremental benefit by tripling the transplantation rate and improving overall survival.
Outcome of liver transplantation for patients infected by hepatitis C, including those infected by genotype 4
Authors: Wali Mohamed H. , Heydtmann Mathis , Harrison Rebecca F. , Gunson Bridget K. , Mutimer David J.
Published: July 2003

Predictors of hepatitis C virus (HCV)-related liver disease posttransplantation are still unclear. The impact of HCV genotype on outcome of transplantation has been studied, but conclusions are not in agreement. The role of HCV genotype 4 on the result of liver transplantation requires further study. The aim of this study is to examine the outcome of liver transplantation for patients with HCV genotype-4 infection. The study group included 128 patients who underwent transplantation for HCV infection: 28 patients, genotype 1; 11 patients, genotype 2; 19 patients, genotype 3; and 32 patients, genotype 4. For 64 of 128 patients, genotype was known and an assessable histological specimen was available. Median interval from transplantation to biopsy was 1.92 years (range, 0.24 to 11.48 years). Twenty-six percent of HCV genotype-4 patients developed either severe fibrosis or cirrhosis versus 6.7% in the genotype non-4 group (P = .04). A statistically significant greater fibrosis progression rate was observed in genotype-4 than genotype non-4 patients. In univariate and multivariate analysis, rapid liver fibrosis was associated with the presence of HCV genotype-4 infection. In addition, donor and recipient age and graft warm ischemic time also were associated with rate of fibrosis progression. Five-year cumulative rates for the development of cirrhosis or severe liver fibrosis were 84% in genotype-4 and 24% in genotype non-4 patients (P = .02). Five-year survival rates for patients with genotypes 1, 2/3, and 4 were 72%, 80%, and 79%, respectively (P = .8). In conclusion, 5-year survival for patients who underwent transplantation for HCV genotype-4 infection was similar to that of genotype non-4 patients; however, more severe fibrosis and rapid fibrosis progression was observed after transplantation in patients with genotype-4 infection.
Histidine-tryptophan-ketoglutarate versus University of Wisconsin solution in living donor liver transplantation: Results of a prospective study
Authors: Testa Giuliano , Malagó Massimo , Nadalin Silvio , Treptow Boris , Paul Andreas , Frilling Andrea , Broelsch Christoph E.
Published: July 2003

The grafts obtained from a living donor hepatectomy are perfused on the back table with either University of Wisconsin solution (UW) or histidine-tryptophan-ketoglutarate solution (HTK). The efficacy and safety of these solutions have been studied in cadaveric liver transplantation, however, there is no study comparing the two solutions in adult-to-adult living donor liver transplantation. In this study, UW and HTK were used in the perfusion of right living donor grafts. The grafts were perfused with a predetermined sequence and volume of one of the solutions. Liver biochemistries, complications, and graft and patient survival were analyzed. From January 2001 to September 2002, 30 grafts were alternately perfused with either UW (UW group) or HTK (HTK group). The perfusion was performed first via the artery and then via the portal vein with a predetermined volume. At a mean follow-up of 13 ± 7 months, no significant statistical difference between groups UW and HTK in posttransplantation liver biochemistries, complications, or patient and graft survival (84% and 80%, respectively) was observed. In conclusion, UW and HTK are equally effective and safe in the perfusion of the living donor liver grafts. HTK has a slight practical advantage over UW because it does not need to be flushed away before reperfusion of the graft and is less expensive.
Arterialized partial orthotopic liver transplantation in the mouse: A new model and evaluation of the critical liver mass
Authors: Tian Yinghua , Graf Rolf , Jochum Wolfram , Clavien Pierre-Alain
Published: July 2003

The availability of a model of partial orthotopic liver transplantation (OLT) in the mouse would be an important tool for studying injuries associated with transplantation. The goals of this study were three-fold: (1) to develop a model of partial OLT in the mouse, (2) to determine the minimal graft volume in this model, and (3) to define the injury associated with small volume incompatible with animal survival. Putative grafts of 30% and 50% were prepared. Their weight was 30 ± 5% and 45 ± 10%, respectively. Subsequently, 30% and 45% syngeneic partial liver grafts were orthotopically transplanted into C57BL/6 mice. Each recipient receiving a 45% graft survived permanently, whereas those receiving only a 30% graft volume died within 2 to 4 days of surgery. Serum transaminase levels normalized in the 45% graft group within 14 days after surgery. In this group, small foci of necrosis and mild steatosis were noted on histology at postoperative day 2, but no abnormalities were noted after 14 days and 100 days. In contrast, recipients who underwent transplantation with a 30% graft volume showed a comparable amount of necrosis and significant microvesicular steatosis in most hepatocytes 2 days after surgery. Hepatocyte proliferation was reduced in this group when compared with animals who underwent transplantation with a 45% graft volume. In conclusion, partial liver transplantation is feasible in the mouse with a critical graft volume ranging between 30% and 45%. Small liver grafts develop massive microvesicular steatosis and impaired regeneration rapidly leading to animal death.
Neutron diffraction studies on aqueous solutions of glucose
Authors: Mason P. E. , Neilson G. W. , Barnes A. C. , Enderby J. E. , Brady J. W. , Saboungi M.-L.
Published: July 2003

Neutron diffraction experiments were carried out at ambient temperature on aqueous solutions of glucose at concentrations of 1, 3, and 5 molal. The difference methods of neutron diffraction and isotopic substitution were used to determine various structure factors associated with all the exchangeable hydrogen atoms of the solutions. The results imply that the hydration of the glucose molecule is not concentration sensitive. It is also found that the average water structure itself is relatively unperturbed by the presence of glucose.
Investigation of spin-polarized resonant tunneling through double-barrier magnetic tunnel junctions by self-consistent solution of the Poisson–Schrödinger equations
Authors: Zervos Matthew
Published: July 2003

Spin-polarized resonant tunneling of electrons through ferromagnet (FM)/insulator, double barrier (DB) magnetic tunnel junctions (MTJs) has been investigated by self-consistent solutions of the Poisson–Schrödinger equations using the transfer matrix method and a realistic band lineup. It is found that significant band bending occurs in the barriers only when the incident electron energy, that falls between the two quasi Fermi levels (FL) of the outer FM layers, is near or at resonance, corresponding to a quasi-bound state in the FM quantum well. As a consequence the potential tends to flatten out in the barriers thereby increasing the resonant energies of the device just below the FL. The tunneling magnetoresistance is thus reduced from 42% to 20% in a Co/5 Å Al2O3/5 Å Co/5 Å Al2O3/Co DBMTJ at an applied bias of 0.2 V after taking into account band bending.
Double tearing mode in plasmas with anomalous electron viscosity
Authors: Dong J. Q. , Mahajan S. M. , Horton W.
Published: July 2003

The linear behavior of the double tearing mode in plasmas with a phenomenological anomalous electron viscosity is investigated within the framework of magnetohydrodynamic theory. In the large Reynolds number R=τv/τh (τv and τh are, respectively, the viscosity penetration time of the magnetic field and the Alfvén time for a plasma sheet of width a) limit, the growth rate is found to scale as R−1/5 if the two resonant surfaces, at x=±xs, are close enough to satisfy xs/a≪(kya)−11/15R−1/15. For larger separation between the resonant surfaces, the growth rate transits to a R−1/3 scaling. The transition occurs at xs/a∼(kya)−11/15R−1/15. The R−1/5 is shown to be closely correlated with the violation of the constant-ψ approximation. The nonlinear velocity perturbations associated with the unstable double tearing mode are estimated to saturate at a level high enough to serve as a trigger for the formation of transport barriers observed in advanced tokamaks.
Degradation mechanism of Schottky diodes on inductively coupled plasma-etched n-type 4H-SiC
Authors: Choi Kyoung Jin , Han Sang Youn , Lee Jong-Lam
Published: July 2003

The degradation mechanism of Ta Schottky contact on 4H-SiC exposed to an inductively coupled plasma (ICP) was studied using deep-level transient spectroscopy and angle-resolved x-ray photoelectron spectroscopy (XPS). Four kinds of traps T1, T2, T3, and T4 were observed in the ICP-etched sample. The T4 trap was deep in the bulk, but the shallower levels, T1, T2 and T3, were localized near the contact. From angle-resolved XPS measurements, the ICP-etched surface was found to be carbon deficient, meaning the production of carbon vacancies by ICP etching. The activation energies 0.48 (T3 trap) and 0.60 eV (T4 trap) agreed well with the previously proposed energy level of VC (0.5 eV). The ICP-induced traps provided a path for the transport of electrons at the interface of metal with SiC, leading to a reduction of the Schottky barrier height and an increase of the gate leakage current.
Misfit dislocation interactions observed by cathodoluminescence in InGaAs on off-cut, patterned GaAs
Authors: Watson George Patrick , Ast Dieter G.
Published: July 2003

Shallow trenches were etched into a substrate of n-type GaAs off-cut from the [001] normal by 5° in both of the perpendicular [110] directions before a lattice mismatched layer of In0.035Ga0.965As was grown. Scanning cathodoluminescence (CL) images of this material show that the misfit dislocations that form to relieve strain are reduced in density to less than 1700 defects/cm compared to over 5000 defects/cm in unpatterned material. The off-cut substrate ensures that the 60° dislocations are no longer parallel, and they can intersect and react to form edge dislocations. These interactions are observed by abrupt changes in line direction and contrast in the CL images. The edge dislocations formed were up to 18 μm long and about 2 μm below the wafer surface until they split again into the original 60° defects. The shape and dimensions of these unique dark line features are in qualitative agreement with calculations based on simple strain energy considerations.
InAs quantum-dot GaAs-based lasers grown on AlGaAsSb metamorphic buffers
Authors: Xin Y.-C. , Vaughn L. G. , Dawson L. R. , Stintz A. , Lin Y. , Lester L. F. , Huffaker D. L.
Published: July 2003

Self-assembled InAs quantum-dot lasers grown by molecular-beam epitaxy using an AlGaAsSb metamorphic buffer layer on a GaAs substrate are reported. The resulting quantum-dot ensemble has a density >3×1010/cm2 and a ground-state transition ranging from 1.46 to 1.63 μm. Pulsed, room-temperature operation generates lasing from the first excited state transition at wavelengths ranging from 1.27 to 1.34 μm. The minimum threshold current density (304 A/cm2) is achieved for a 7.7 mm cavity with cleaved, uncoated facets.
Hall magnetohydrodynamics of neutral layers
Authors: Huba J. D. , Rudakov L. I.
Published: July 2003

New analytical and numerical results of the dynamics of inhomogeneous, reversed field current layers in the Hall limit (i.e., characteristic length scales ≲ the ion inertial length) are presented. Specifically, the two- and three-dimensional evolution of a current layer that supports a reversed field plasma configuration and has a density gradient along the current direction is studied. The two-dimensional study demonstrates that a density inhomogeneity along the current direction can dramatically redistribute the magnetic field and plasma via magnetic shock-like or rarefaction waves. The relative direction between the density gradient and current flow plays a critical role in the evolution of the current sheet. One important result is that the current sheet can become very thin rapidly when the density gradient is directed opposite to the current. The three-dimensional study uses the same plasma and field configuration as the two-dimensional study but is also initialized with a magnetic field perturbation localized along the current channel upstream of the plasma inhomogeneity. The perturbation induces a magnetic wave structure that propagates in the direction of the electron drift (i.e., opposite to the current). The propagating wave structure is a Hall phenomenon associated with magnetic field curvature. The interaction between the propagating wave structure and the evolving current layer can lead to rapid magnetic field line reconnection. The results are applied to laboratory and space plasma processes.
Modulation of the electronic properties of GaN films by surface acoustic waves
Authors: Camacho J. , Santos P. V. , Alsina F. , Ramsteiner M. , Ploog K. H. , Cantarero A. , Obloh H. , Wagner J.
Published: July 2003

We report on the interaction between photogenerated electron-hole pairs and surface acoustic waves (SAW) in GaN films grown on sapphire substrates. The spatial separation of photogenerated carriers by the piezoelectric field of the SAW is evidenced by the quenching of the photoluminescence (PL) intensity. The quenching levels in GaN are significantly smaller than those measured in GaAs under similar conditions. The latter is attributed to the lower exciton ionization efficiency and carrier separation probabilities mediated by the piezoelectric effect. The PL spectra also evidence energy shifts and broadenings of the electronic transitions, which are attributed to the band gap modulation by the SAW strain field.
Optical properties of strained antimonide-based heterostructures
Authors: Dinu M. , Cunningham J. E. , Quochi F. , Shah J.
Published: July 2003

The optical properties of strained GaAsSb/GaAs quantum wells grown by molecular beam epitaxy were investigated by photoluminescence spectroscopy as a function of excitation intensity and temperature. Photoluminescence spectra exhibit strong blue shifts of the emission peak with increasing excitation intensity, ascribed to the interplay between band tail filling at low carrier densities and electrostatic band bending at high carrier concentrations. Spectroscopic data are consistent with a type II band alignment, with a small conduction band offset (ΔEc∼100 meV), and gain spectra are blue shifted with respect to the low excitation luminescence. The large material gain and fast carrier recombination lifetimes demonstrate the viability of this material system for the fabrication of 1.3 μm lasers.
Scattering of dust ion acoustic wave off a dust acoustic wave
Authors: Annou R. , Bharuthram R. , Bahamida S.
Published: July 2003

The scattering of dust ion acoustic mode off a dust acoustic mode, where dust charge fluctuation is taken into account self-consistently, is investigated. It is shown that above threshold, parametric generation of dust acoustic waves occurs. The nonlinear growth rate and excitement threshold are determined. The relevance to parametric instabilities saturation via cascading of sidebands to lower frequency modes is pointed out.
Painlevé analysis of the Ricci-flat ordinary differential equations associated with Aloff–Wallach spaces and U(1)-bundles over Fano products
Authors: Dancer Andrew , Wang McKenzie Y.
Published: July 2003

We apply techniques of Painlevé–Kowalewski analysis to certain ODE reductions of the Ricci-flat equations. We particularly focus on two examples when the hypersurface is an Aloff–Wallach space or a circle bundle over a Fano product.
Polyhedral scattering of fundamental monopoles
Authors: Battye Richard A. , Gibbons Gary W. , Rychenkova Paulina , Sutcliffe Paul M.
Published: July 2003

The dynamics of n slowly moving fundamental monopoles in the SU(n+1) BPS Yang–Mills–Higgs theory can be approximated by geodesic motion on the 4n-dimensional hyperkähler Lee–Weinberg–Yi manifold. In this article we apply a variational method to construct some scaling geodesics on this manifold. These geodesics describe the scattering of n monopoles which lie on the vertices of a bouncing polyhedron; the polyhedron contracts from infinity to a point, representing the spherically symmetric n-monopole, and then expands back out to infinity. For different monopole masses the solutions generalize to form bouncing nested polyhedra. The relevance of these results to the dynamics of well separated SU(2) monopoles is also discussed.
Icosahedral Skyrmions
Authors: Battye Richard A. , Houghton Conor J. , Sutcliffe Paul M.
Published: July 2003

In this article we aim to determine the baryon numbers at which the minimal energy Skyrmion has icosahedral symmetry. By comparing polyhedra which arise as minimal energy Skyrmions with the dual of polyhedra that minimize the energy of Coulomb charges on a sphere, we are led to conjecture a sequence of magic baryon numbers, B=7,17,37,67,97,…, at which the minimal energy Skyrmion has icosahedral symmetry and unusually low energy. We present evidence for this conjecture by applying a simulated annealing algorithm to compute energy minimizing rational maps for all degrees up to 40. Further evidence is provided by the explicit construction of icosahedrally symmetric rational maps of degrees 37, 47, 67 and 97. To calculate these maps we introduce two new methods for computing rational maps with Platonic symmetries.
Effects of the radial plasma-wall interaction on the Hall thruster discharge
Authors: Ahedo E. , Gallardo J. M. , Martı́nez-Sánchez M.
Published: July 2003

The interaction of the plasma discharge with the ceramic walls of a Hall thruster leads to plasma recombination, energy losses, and extra electron collisionality. These three phenomena are included in a one-dimensional axial model of the discharge through source terms obtained from an auxiliary model of the radial dynamics. Spatial solutions are presented for different discharge voltages and wall materials, and agree satisfactorily with experimental data. The parameters related to wall effects are investigated extensively. The energy balance among Joule heating, wall-losses cooling, and heat conduction shapes the temperature profile; three different profile types are identified depending on the wall material and the discharge voltage. For long chambers, the main source of energy losses is the plasma interaction with the walls, even for zero secondary electron emission. By contrast, wall collisionality due to primary/secondary exchanges of electrons is negligible always. The current utilization is related directly to the total energy losses. The propellant utilization is set by the balance between gas ionization and wall recombination in the acceleration region. The rate of wall recombination suggested by the axial solution is much lower than the values given by radial models based on a Maxwellian electron distribution function.
Anisotropic weak whistler wave turbulence in electron magnetohydrodynamics
Authors: Galtier S. , Bhattacharjee A.
Published: July 2003

A weak wave turbulence theory is given for electron magnetohydrodynamics in the presence of a strong and uniform external magnetic field. Using helicity decomposition, the wave kinetic equations for energy and magnetic helicity are derived at the level of three-wave interactions between whistler waves. It is shown that nonlinear interactions of whistler waves transfer energy and magnetic helicity mainly in the direction perpendicular to the external magnetic field. The anisotropic turbulence thus generated has exact stationary power law solutions which scale as k⊥−5/2k∥−1/2 for the energy spectrum and k⊥−7/2k∥−1/2 for the magnetic helicity spectrum.
The moduli space of noncommutative vortices
Authors: Tong David
Published: July 2003

The Abelian Higgs model on the noncommutative plane admits both BPS vortices and non-BPS fluxons. After reviewing the properties of these solitons, we discuss several new aspects of the former. We solve the Bogomoln’yi equations perturbatively, to all orders in the inverse noncommutivity parameter, and show that the metric on the moduli space of k vortices reduces to the computation of the trace of a k×k-dimensional matrix. In the limit of large noncommutivity, we present an explicit expression for this metric.
Topological Q-solitons
Authors: Ward R. S.
Published: July 2003

Static topologically-nontrivial configurations in sigma-models, for spatial dimension D⩾2, are unstable. The question addressed here is whether such sigma-model solitons can be stabilized by steady rotation in internal space; that is, rotation in a global SO(2) symmetry. This is the mechanism which stabilizes Q-balls (nontopological solitons). The conclusion is that the Q-mechanism can stabilize topological solitons in D=2 spatial dimensions, but not for D=3.
Electron acceleration by a stochastic electric field in the atmospheric layer
Authors: Trakhtengerts Victor Y. , Iudin Dmitriy I. , Kulchitsky Anton V. , Hayakawa Masashi
Published: July 2003

Electron acceleration by a stochastic (in space) electric field is considered in the atmosphere taking into account limited scales of the acceleration layer. The general kinetic equation for the isotropic part of the electron distribution function is thereby derived, which includes runaway effects and influence of a stochastic electric field on spatial diffusion. A tail of accelerated electrons in the distribution function appears when the electric field intensity overtakes the threshold value, which is close to the threshold in a constant electric field. Stationary solutions of the kinetic equation in a finite layer are analyzed numerically in the presence of source of energetic electrons. These solutions are discussed in connection with γ- and x-ray emissions observed inside thunderclouds.
Apertureless near-field optical microscopy: A study of the local tip field enhancement using photosensitive azobenzene-containing films
Authors: Bachelot Renaud , H’Dhili Fekhra , Barchiesi Dominique , Lerondel Gilles , Fikri Radouane , Royer Pascal , Landraud Nathalie , Peretti Jacques , Chaput Frédéric , Lampel Georges , Boilot Jean-Pierre , Lahlil Khalid
Published: July 2003

The local optical field enhancement which can occur at the end of a nanometer-size metallic tip has given rise to both increasing interest and numerous theoretical works on near-field optical microscopy. In this article we report direct experimental observation of this effect and present an extensive study of the parameters involved. Our approach consists in making a “snapshot” of the spatial distribution of the optical intensity in the vicinity of the probe end using photosensitive azobenzene-containing films. This distribution is coded by optically induced surface topography which is characterized in situ by atomic force microscopy using the same probe. We perform an extensive analysis of the influence of several experimental parameters. The results are analyzed as a function of the illumination parameters (features of the incident laser beam, exposure time, illumination geometry) as well as the average tip-to-sample distance and tip geometry. The results obtained provide substantial information about the tip’s field. In particular, they unambiguously demonstrate both the nanometric spatial confinement of the tip field and the evanescent nature of the nanosource excited at the tip’s end. Most of the experimental results are illustrated by numerical calculations based on the finite element method and commented using the literature on the subject. Additionally, we discuss the origin of the optically induced topography on a nanometer scale and present some preliminary results of the apertureless near-field optical lithography based on local field enhancement. Our approach constitutes a useful tool to investigate the near-field of apertureless probes and should enable the optimization of the nanosource for any experiment requiring local optical excitation of the matter.
Coupled third harmonic generations and multiple mode effects in aperiodic optical superlattices with a finite lateral width
Authors: Zhao Li-Ming , Gu Ben-Yuan , Zhou Yun-Song , Wang Fu-He
Published: July 2003

We study the coupled third harmonic generations (CTHGs) from quasi-one-dimensional aperiodic optical superlattices (AOSs) with a finite lateral width. We design the special AOS that can implement multiple wavelength CTHG with identical effective nonlinear coefficient at the preassigned wavelengths of incident light with the use of simulated annealing method. We reveal the effects of mode-mode coupling and the lateral width of the AOSs on the CTHG for the two cases: One case corresponds to the incident light beam of a plane wave profile and other case to the incident light beam of Gaussian profile. The results show that the characteristics of the CTHG from the AOSs are closely related to the profiles of the incident fundamental frequency light beam. For the incidental plane wave beam, the dependence of the effective nonlinear coefficient on the width of the AOS is quite weak. On the contrary, for the incident Gaussian profile beam, this dependence exhibits a rapid decrease at the beginning and then tends to a constant. We also display the variation of the effective nonlinear coefficients with the optical wave propagating distance from the impinging surface of incident light beam in the sample illuminating by the plane wave light beam and find that this variation exhibits basically increasing behavior. This clearly infers that the contribution of every individual block to optical CTHG process is a constructive addition. When increasing the number of the modes, the effective nonlinear coefficient of CTHG is rapidly decreased at the beginning and it then tends to a saturation value for the incident plane wave light beam. However, for the incident light beam of Gaussian profile, similar behavior is observed only when the lateral width of the AOS is smaller than that of the Gaussian profile beam; in contrast, the Nc dependence of the effective nonlinear coefficient of the CTHG is quite weak.