bluuebunny/crossref_metadata_2025 huggingface dataset:
Preoperative Therapy With Trastuzumab and Paclitaxel Followed by Sequential Adjuvant Doxorubicin/Cyclophosphamide for HER2 Overexpressing Stage II or III Breast Cancer: A Pilot Study
Authors: Burstein Harold J. , Harris Lyndsay N. , Gelman Rebecca , Lester Susan C. , Nunes Raquel A. , Kaelin Carolyn M. , Parker Leroy M. , Ellisen Leif W. , Kuter Irene , Gadd Michele A. , Christian Roger L. , Kennedy Patricia Rae , Borges Virginia F. , Bunnell Craig A. , Younger Jerry , Smith Barbara L. , Winer Eric P.
Published: December 2002

Purpose: Trastuzumab combined with chemotherapy improves outcomes for women with human epidermal growth factor receptor 2 (HER2) overexpressing advanced breast cancer. We conducted a pilot study of preoperative trastuzumab and paclitaxel, followed by surgery and adjuvant doxorubicin and cyclophosphamide chemotherapy in earlier stage breast cancer.

Patients and Methods: Patients with HER2-positive (2+ or 3+ by immunohistochemistry) stage II or III breast cancer received preoperative trastuzumab (4 mg/kg × 1, then 2 mg/kg/wk × 11) in combination with paclitaxel (175 mg/m2 every 3 weeks × 4). Patients received adjuvant doxorubicin and cyclophosphamide chemotherapy following definitive breast surgery. Clinical and pathologic response rates were determined after preoperative therapy. Left ventricular ejection fraction and circulating levels of HER2 extracellular domain were measured serially.

Results: Preoperative trastuzumab and paclitaxel achieved clinical response in 75% and complete pathologic response in 18% of the 40 women on study. HER2 3+ tumors were more likely to respond than 2+ tumors (84% v 38%). No unexpected treatment-related noncardiac toxicity was encountered. Four patients developed grade 2 cardiotoxicity (asymptomatic declines in left ventricular ejection fraction). Baseline HER2 extracellular domain was elevated in 24% of patients and declined with preoperative therapy. Immunohistochemical analyses of posttherapy tumor specimens indicated varying patterns of HER2 expression following trastuzumab-based treatment.

Conclusion: Preoperative trastuzumab and paclitaxel is active against HER2 overexpressing early-stage breast cancer and may be feasible as part of a sequential treatment program including anthracyclines. The observed changes in cardiac function merit further investigation. Correlative analyses of HER2 status may facilitate understanding of tumor response and resistance to targeted therapy.
Prognostic Factors and Clinical Outcomes in Children and Adolescents With Metastatic Rhabdomyosarcoma—A Report From the Intergroup Rhabdomyosarcoma Study IV
Authors: Breneman John C. , Lyden Elizabeth , Pappo Alberto S. , Link Michael P. , Anderson James R. , Parham David M. , Qualman Stephen J. , Wharam Moody D. , Donaldson Sarah S. , Maurer Harold M. , Meyer William H. , Baker K. Scott , Paidas Charles N. , Crist William M.
Published: December 2002

Purpose: To identify risk factors associated with outcomes in children with metastatic rhabdomyosarcoma (RMS) treated on the fourth Intergroup Rhabdomyosarcoma Study (IRS-IV).

Patients and Methods: Patients with metastatic RMS were treated with one of two regimens that incorporated a window of either ifosfamide and etoposide (IE) with vincristine, dactinomycin, and cyclophosphamide (VAC) or vincristine, melphalan (VM) and VAC. Study end points were failure-free survival (FFS) and overall survival (OS). Clinical factors including age, histology, sites of primary and metastatic disease, and number of sites of metastatic disease were correlated with those end points.

Results: One hundred twenty-seven patients were eligible for analysis. The estimated 3-year OS and FFS for all patients were 39% and 25%, respectively. By univariate analysis, 3-year OS was significantly influenced by histology (47% for embryonal v 34% for all others, P = .026) and increasing number of metastatic sites (P = .028). By multivariate analysis, the presence of two or fewer metastatic sites was the only significant predictor (P = .007 and .006, respectively). The combination of embryonal histology with two or fewer metastatic sites identified a subgroup with 3-year FFS of 40% and OS of 47%.

Conclusion: Children with group IV RMS treated on the IRS-IV study had improved OS and FFS if they had two or fewer metastatic sites and embryonal histology. This favorable subset of patients has outcomes approaching those observed in selected patients with localized, nonmetastatic disease. Thus, these patients might not be appropriate candidates for regimens that include experimental agents with substantial toxicities or unproven antitumor activity.
Thermodynamic determination of β‐hexosaminidase isoenzymes in mononuclear and polymorphonuclear leukocyte populations
Authors: Casal J. Antonio , Chabás Amparo , Tutor J. Carlos
Published: December 2002

Isoenzymes of β‐hexosaminidase (Hex) were determined in mononuclear (MN) and polymorphonuclear (PMN) leukocytes, with a thermodynamic method using the chromogenic substrate sodio‐3,3′‐dichlorophenolsulfonphthaleinyl N‐acetyl‐β‐D‐glucosaminide. Imprecision was very satisfactory, and the results are very much in agreement with those obtained using the fluorogenic substrates 4‐methylumbelliferyl N‐acetyl‐β‐D‐glucosaminide and 4‐methylumbelliferyl N‐acetyl‐β‐D‐glucosaminide 6‐sulfate. In 163 healthy individuals we found, for the proportion as a percentage of the Hex A isoenzyme, significantly higher values (P < 0.001) in PMN than in MN cells (71.56 ± 0.30% vs. 54.28 ± 0.24%), meaning that it would not appear advisable to use total leukocyte lysates for evaluating this variable. The method is fast, precise, and highly suitable for the biochemical diagnosis and heterozygote screening of GM2 gangliosidoses, and would be applicable in cases of thermolabile Hex B and for detecting the B1 variant. © 2002 Wiley‐Liss, Inc.
Transcriptionally mediated gene targeting of gas1 to glioma cells elicits growth arrest and apoptosis
Authors: Zamorano Absalom , Lamas Mónica , Vergara Paula , Naranjo José R. , Segovia José
Published: December 2002

Induction of growth arrest‐specific genes (gas1) prevents cell proliferation and/or leads to apoptosis in different cell types. In neurons, it has been recently reported that mild excitotoxic neuronal death is associated with gas1 induction, and that overexpression of Gas1 induces apoptosis in terminally differentiated neurons or in proliferating neuroblastoma cells. In the present study, we have analysed the effects of the transcriptionally mediated targeting of gas1 to C6 rat glioma cells. Expression of Gas1 decreased glial proliferation and induced C6 cell apoptosis. While the identity of the caspase(s) responsible for Gas1‐induced apoptosis in neurons has remained elusive, in C6 glioma cells, overexpression of Gas1 reproducibly activated caspase‐3. Our results support the concept of targeted expression of gas1 as a potentially useful gene therapy strategy in the treatment of human gliomas. © 2002 Wiley‐Liss, Inc.
The Structure and Morphotectonics of the Gesher Benot Ya'aqov Area, Northern Dead Sea Rift, Israel
Authors: Belitzky Shmuel
Published: December 2002

Geological, geomorphological, and morphotectonic studies at the Gesher Benot Ya'aqov Acheulean site, Northern Jordan Valley, provide: 1) a unique opportunity to establish the ecological background of hominid behavior during the early stages of widespread human occupation; 2) crucial data for understanding the paleo-environment and the various processes that affected the area near the Gesher Benot Ya'aqov site; and 3) a basis for further comprehensive research in the region.

Quaternary tectonic activity near the Acheulean archeological site has produced a complex local setting that controls the surrounding landscape. Tectonic activity formed the Benot Ya'aqov embayment, which attracted hominids and a variety of other fauna. Sediments of the Benot Ya'akov formation deposited in the embayment facilitated excellent preservation of the remnants of Acheulean hominid activities and of abundant floral and faunal remains. The formation was subsequently affected by faulting and folding. Local uplift ended the deposition of lacustrine sediments in the embayment of Hula Valley Basin and caused erosion and vertical incision of the Jordan River that resulted in the capture of the Rosh Pinna River and the exposure of the Benot Ya'akov formation. These deposits are found in different structural positions along the north–south oriented morphotectonic embayment. The outcrops contain numerous archeological sites, giving the study area an unusually high potential for future hominid discoveries.
Impact of the Late Glacial Eruption of the Laacher See Volcano, Central Rhineland, Germany
Authors: Baales Michael , Jöris Olaf , Street Martin , Bittmann Felix , Weninger Bernhard , Wiethold Julian
Published: December 2002

Within a period of a few weeks toward the end of the Allerød Interstadial, the major Plinian eruption of the Laacher See volcano produced some 20 km3of eruptiva, covering and preserving the late-glacial landscape in the German Central Rhineland over an area of more than 1000 km2. Correlation of terrestrial archives with the Greenland ice-core records and improved calibration of the radiocarbon timescale permit a precise, accurate age determination of the Laacher See event some 200 yr before the onset of the Younger Dryas cold episode. Carbonized trees and botanical macrofossils preserved by Laacher See Tephra permit detailed regional paleoenvironmental reconstruction and show that open woodland were typical for the cool and humid hemiboreal climatic conditions during the late Allerød. This woodland provided the habitat for a large variety of animal species, documented at both paleontological and Final Paleolithic archeological sites preserved below Laacher See deposits. Of special interest are numerous animal tracks intercalated in Middle Laacher See deposits at the south of the Neuwied Basin. This knowledge may help to evaluate possible supraregional impacts of this volcanic event on northern hemispheric environment and climate during the late Allerød.
Morphological Chronoclines among Late Pleistocene Muskrats (Ondatra zibethicus: Muridae, Rodentia) from Northern Florida
Authors: Mihlbachler Matthew C. , Hemmings C. Andrew , Webb S. David
Published: December 2002

The muskrat (Ondatra zibethicus) is presumed to have undergone a rapid phyletic size decrease near the end of the Pleistocene. Evolutionary changes in the size of middle to late Wisconsinan (ca. 32,000–12,30014C yr B.P.) muskrats from the Aucilla River, Jefferson County, Florida, were reconstructed by examining length and width of the lower first molar (m1). Body mass, estimated from m1 length, was relatively stable from 32,000 to 16,00014C yr B.P. and decreased only slightly by 12,30014C yr B.P. If the size trend found in the Aucilla River material is characteristic of the southeastern United States, a body size decrease after 12,30014C yr B.P. is needed to explain the smaller size of modern populations. It was previously thought that the length/width (l/w) ratio of the muskrat m1 was a paleoenvironmental indicator based on its presumed correlation with latitude in modern populations. We examined the length and width of modern muskrats from several geographic regions and found only a very weak trend in the size of the m1 between northern and southern populations; however, highly significant differences were found between regions of similar latitude. Our data indicate that chronoclines in the m1 of the Aucilla muskrat material and other such documented trends among fossil muskrats have paleoenvironmental significance, but it is not yet clear which environmental variables can best be predicted from them.
The physical state of the LDL core influences the conformation of apolipoprotein B‐100 on the lipoprotein surface
Authors: Coronado-Gray Andrea , van Antwerpen Rik
Published: December 2002

We assessed the influence of temperature on the secondary structure of apolipoprotein B‐100 (apoB) in normal low‐density lipoprotein (N‐LDL) and triglyceride‐rich LDL (T‐LDL). Gradual heating from 7°C to the phase‐transition temperature of the lipoprotein core (∼28°C and ∼15°C for N‐LDL and T‐LDL, respectively) gradually altered the secondary structure of apoB, while further heating from the phase‐transition temperature to 45°C had no additional effect. Above the phase‐transition temperature of the core, the apoBs of N‐LDL and T‐LDL had a similar secondary structure. These results indicate that the conformation of apoB on the LDL surface depends strongly on the physical state of the lipoprotein core, and less on the lipid composition of the core per se.
Screening for domestic violence among patients admitted to a French emergency service
Authors: Lejoyeux Michel , Zillhardt Patrick , Chièze François , Fichelle Anika , Mc Loughlin Mary , Poujade Astrid , Adès Jean
Published: December 2002

Objective.

The authors assessed the prevalence of domestic violence among patients examined in the emergency service of a general hospital. They compared the socio-demographic status and psychiatric comorbidity of victims of domestic violence and other patients.

Method.

An assessment was made on 126 consecutive patients received by the emergency service of Bichat-Claude Bernard hospital (Paris, France). Assessment of domestic violence was made through the use of a specific questionnaire.

Results.

The prevalence rate of domestic violence was 18% among patients examined by the emergency service. Thirty-five percent of the cases were physical violence, 22% sexual violence, 17% psychological violence and 26% multiple forms of domestic violence. Domestic violence had been going on for less than 1 month in only one case. In 74% of the cases, violence lasted for more than 1 year. No differences were found in terms of socio-demographic characteristics (age, marital status, rate of unemployment, sex ratio) and psychiatric comorbidity between victims of domestic violence and others.

Conclusion.

Patients seen in an emergency service must be identified as a population at risk for domestic violence (18%). These situations can be identified only by a systematic assessment using a standardized questionnaire.
Prolidase deficiency diagnosed by 1H NMR spectroscopy of urine
Authors: Moolenaar S. H. , Engelke U. F. H. , Abeling N. G. G. M. , Mandel H. , Duran M. , Wevers R. A.
Published: December 2002

Three urine samples from two prolidase‐deficient patients were analysed using 1H NMR spectroscopy. One‐dimensional 1H NMR spectra showed a characteristic pattern of overlapping resonances of the proline and hydroxyproline protons of the imidodipeptides. The model compounds Ala‐Pro, Gly‐Pro, Phe‐Pro, Leu‐Pro, Val‐Pro, Gly‐Hyp and Pro‐Hyp were measured as well. The non‐proline resonances of Val‐Pro, Ala‐Pro and Gly‐Pro could be assigned in the urine spectra. These resonances could then be used for quantification of the corresponding imidodipeptids. The presence of Leu‐Pro in the patients' urine was demonstrated by the results of COSY experiments. However, this imidodipeptide could not be quantified owing to overlap of the resonaces in the one‐dimensional 1H NMR spectrum of the patients' urine. Phe‐Pro, Pro‐Hyp and Gly‐Hyp could not be assigned in the spectrum of the patient's urine. The characteristic resonances in the urine from a prolidase‐deficient patient, i.e. Ala‐Pro, Val‐Pro, Gly‐Pro, and resonances of the (hydroxy)proline part of the imidodipeptides can be used to diagnose this disease.
cAMP-Dependent Protein Kinase Inhibits Proline Transport Across the Rat Renal Tubular Brush Border Membrane
Authors: Zelikovic Israel , Wager-Miller James
Published: December 2002

Very little is known about the cellular mechanisms controlling renal tubular amino acid transport. cAMP-dependent protein kinase (cAK) modulates the activity of several ion channels and pumps in biological membranes. The direct influence of cAK on transmembrane amino acid transport has not been investigated. We studied the effect the cAK-mediated phosphorylation on Na+- and Cl−-linked proline transport across the rat renal brush border membrane (BBM). cAK bioassay and Western hybridization analysis using cAK subunit-specific antibodies demonstrated the presence of the enzyme in the BBM. Brush border membrane vesicles (BBMV) were phosphorylated using the “hyposmotic shock” technique. cAMP, by activating endogenous cAK, and exogenous, highly purified catalytic subunit of cAK inhibited NaCl-dependent proline transport by phosphorylated, lysed/resealed BBMV compared with control vesicles. The cAK-mediated inhibition of proline uptake was completely abolished when phosphorylation at the cytoplasmic (inner side) of the membrane was prevented by isosmotic, rather than hyposmotic, phosphorylation. The cAK-induced inhibition of proline transport was reversed by the specific cAK inhibitor peptide, PKl. These data suggest that cAMP-dependent protein kinase-mediated phosphorylation modulates Na+- and Cl−-linked proline transport across the tubular luminal membrane.
Social support and problem‐solving as moderators of the relationship between childhood abuse and suicidality: Applications to a delinquent population
Authors: Esposito Christianne L. , Clum George A.
Published: December 2002

The purpose of the current study was to examine the relationship between childhood abuse, social support, and problem‐solving appraisal within a juvenile delinquent sample. Hierarchical regression analyses were used to assess whether childhood abuse, social support, and problem‐solving appraisal were independently predictive of suicidality, and further, whether problem‐solving appraisal and social support moderated the childhood abuse–suicidality relationship. Childhood sexual abuse was found to be an independent predictor of suicidal ideation and behavior. In addition, both problem‐solving confidence and social support moderated the relationship between childhood abuse and suicidal ideation. The results of this study underscore the importance of both problem‐solving appraisal and social support to suicidality in adolescents with a history of abuse.
Plasma Lysine Concentration and Availability of 2‐Ketoglutarate in Liver Mitochondria
Authors: Kamoun P. , Richard V. , Rabier D. , Saudubray J. M.
Published: December 2002

Defects of lysine metabolism are rare, but hyperlysinemia is a concomitant of many inborn errors of metabolism, including urea cycle abnormalities, pyruvate carboxylase deficiency and L‐2‐hydroxyglutaric aciduria. We have hypothesized that mitochondrial lysine degradation is regulated by bioavailability of 2‐oxoglutarate in the same compartment, and our studies in physiologic fluid derived from patients with the above described disorders supports our hypothsis. Our data further suggest that patients with isolated L‐2‐hydroxyglutaric aciduria may have a defect in 2‐ketoglutarate metabolism. The current report summarizes our studies.
The natural history of acute histologic rejection without biochemical graft dysfunction in orthotopic liver transplantation: A systematic review
Authors: Bartlett Adam S. , Ramadas Ravi , Furness Sue , Gane Ed , McCall John L.
Published: December 2002

Protocol biopsy results in the first few weeks after liver transplantation sometimes display histologic features of acute cellular rejection (ACR), even in the absence of significant clinical or biochemical dysfunction. At present there is no clear consensus about the need to treat such cases with adjuvant immunosuppression. This systematic review describes, from the available evidence, the natural history of untreated histologic ACR in the absence of biochemical graft dysfunction. An electronic search of the Medline, Embase, and Cochrane Library databases was performed to select studies that reported protocol liver biopsies in the early posttransplant period from 1983 to 2000. Studies that identified patients with ACR on protocol biopsy who were not treated with adjuvant immunosuppression formed the basis of the study group. Data from individual studies were extracted using standardized pro forma and pooled for descriptive analysis. The search identified 3431 studies, of which 516 were cited in full. Of these, 15 studies met all of the inclusion criteria. These 15 studies reported on 1566 patients who had protocol biopsies performed in the early posttransplant period, of which 1048 (67%) had histologic evidence of ACR. Three hundred and thirty one (32%) patients with histologic ACR on protocol biopsy had no associated biochemical graft dysfunction. Without treatment, only 14% of these patients subsequently developed biochemical graft dysfunction requiring adjuvant immunosuppression. Steroid-resistant rejection and chronic rejection both had a prevalence of 4% in patients with untreated histologic ACR and no biochemical graft dysfunction. Withholding adjuvant immunosuppression from patients with histologic ACR and no biochemical graft dysfunction seems to be safe, as long as graft function is carefully monitored. The rationale for performing protocol biopsies in the absence of biochemical graft dysfunction is questionable.
Percutaneous radiofrequency thermal ablation of hepatocellular carcinoma: A safe and effective bridge to liver transplantation
Authors: Fontana Robert J. , Hamidullah Halimi , Nghiem Hanh , Greenson Joel K. , Hussain Hero , Marrero Jorge , Rudich Steve , McClure Leslie A. , Arenas Juan
Published: December 2002

The incidence of hepatocellular carcinoma (HCC) is increasing in the United States. Although liver transplantation is an effective means of treating selected patients, pretransplantation tumor progression may preclude some patients from undergoing transplantation. The aim of this study is to determine the safety and efficacy of percutaneous radiofrequency thermal ablation (RFA) in 33 consecutive patients with nonresectable HCC and advanced cirrhosis. Mean subject age was 57.2 ± 10.6 years, mean Child-Turcotte-Pugh score was 7.0 ± 1.4, and mean maximal tumor diameter was 3.6 ± 1.1 cm. Using contrast-enhanced computed tomography and magnetic resonance imaging, 22 patients (66%) had a complete radiological response at 3 months post-RFA, whereas 11 patients (33%) had an incomplete radiological response. During follow-up, 18 patients (54%) experienced tumor progression and 9 subjects underwent repeated ablation for either residual disease or tumor progression. The overall actuarial patient survival rate of the 33 patients was 58% at 2 years, whereas the transplantation-free patient survival rate was 34% at 2 years. Fifteen of 23 transplant candidates were successfully bridged to liver transplantation after a mean post-RFA follow-up of 7.9 ± 6. 7 months. The extent of tumor necrosis in the explant varied, but no subjects had evidence of tumor seeding on post-RFA imaging, at liver transplantation, or in the explant. The 3-year actuarial posttransplantation patient survival rate was 85%. Two patients have developed posttransplantation recurrence, and both had microscopic vascular invasion in their explants. In summary, our data show that RFA is a safe and effective treatment modality for patients with advanced cirrhosis and nonresectable HCC. Although the ability of RFA to prevent or delay tumor progression requires further prospective study, its favorable safety profile and promising efficacy make it an attractive treatment option for liver transplant candidates with nonresectable HCC.
Dependence of the interfacial capacitance on measurement regime used for investigation of thin film ferroelectric capacitors
Authors: Sinnamon L. J. , McAneney J. , Bowman R. M. , Gregg J. M.
Published: December 2002

Thin film parallel-plate capacitor structures with Ba0.5Sr0.5TiO3 as the dielectric layer were fabricated using pulsed-laser deposition. The thickness of the dielectric was varied between 7.5 nm and 1.4 μm. Low-field measurements of the dielectric constant showed the system to possess a nonzero interfacial capacitance. Since there is considerable debate about the origin of interfacial capacitance, further functional analysis was performed: zero-field dielectric susceptibility information was extracted using Landau–Ginzburg–Devonshire fitting of saturated polarization loops. This analysis revealed that the zero-field dielectric susceptibility extracted from P–E loops does not possess a finite interfacial component. The origin of interfacial capacitance therefore disappears (albeit temporarily) after a significant field has been applied and then removed during the P–E loop measurement cycle.
Photodissociation of the ArHBr complex investigated with the multiconfiguration time-dependent Hartree approach
Authors: Trin J. , Monnerville M. , Pouilly B. , Meyer H.-D.
Published: December 2002

We apply the multiconfiguration time-dependent Hartree method to the study of the photodissociation of the Ar–HBr van der Waals complex. The dynamics is studied in both Jacobi and valence coordinates. The evolution of the probability density in the different modes shows that the direct or nearly direct mechanism, where the hydrogen atom interacts only very weakly with the Ar and Br atoms, dominates the dissociation process. By projecting the quantum flux onto the vibrational levels of ArBr, we find at the maximum of the absorption profile, i.e., around E=3 eV, that 65% of the dissociation gives rise to partial fragmentation into hot H fragments and bound ArBr molecules.
Analytical time-dependent Hartree-Fock evaluation of the dynamic zero-point vibrationally averaged (ZPVA) first hyperpolarizability
Authors: Quinet Oliver , Kirtman Bernard , Champagne Benoı̂t
Published: December 2002

A procedure to compute analytical second derivatives of the dynamic first hyperpolarizability with respect to vibrational coordinates has been developed and implemented at the time-dependent Hartree-Fock level. Simplifications are obtained by the same techniques as those employed to derive the 2n+1 rule and the interchange relations. This scheme is used to determine the first-order ZPVA correction for three small molecules. It is found that the frequency dispersion coefficients are similar to those obtained for the pure electronic contribution in H2O and NH3 but not CH4.
Brownian dynamics simulations of polymer stretching and transport in a complex electroosmotic flow
Authors: Panwar Ajay S. , Kumar Satish
Published: December 2002

Brownian dynamics simulations are performed to study the stretching and transport of flexible polymers in complex electroosmotic flows. The flows are generated by prescribing a spatially periodic charge distribution on the walls of a parallel-plate channel and applying an electric field parallel to the direction of charge modulation. The polymer molecules are modeled as bead–spring chains and the model parameters are chosen to be representative of DNA. Simulations are performed for the cases of uncharged and charged polymers. For the uncharged case, it is found that the stagnation point in the center of the flow is not effective at stretching the polymers due to the fact that the flow has an inhomogeneous velocity gradient. It is observed that polymers tend to become trapped in the recirculation rolls near that stagnation point, and that the amount of stretching that does occur is directly proportional to the amount of time that the polymer spends near the stagnation point at the wall. For the charged case, it is found that the trapping persists below a critical charge density, but that above this threshold the polymer escapes from the rolls. Our observations suggest that while these complex flows may not be useful for stretching polymers far away from the channel walls, they may be useful for localizing the position of Brownian particles in microfluidic devices. In addition, they illustrate the rich dynamics that arise when polymers are placed in flows with inhomogeneous velocity gradients and when electroosmotic flow competes with electrophoresis.
Collapse transition for isolated square-well chain molecules: The exact density of states for short chains
Authors: Taylor Mark P.
Published: December 2002

In this work we study isolated flexible interaction-site chain molecules comprised of n square-well-sphere monomers. We compute the “exact” density of states of such chains with n=3, 4, 5, and 6 and use these results to carry out a detailed study of the thermodynamics of chain collapse. We find that for a certain range of square-well diameters both the n=5 and 6 chains undergo a multistage collapse transition with decreasing temperature (as indicated by multiple peaks in the specific heat and, in some cases, by discrete steps in the internal energy). The collapse behavior is strongly affected by the presence of a set of “cut-off” values of the square-well diameter at which the ground-state energy of the chain undergoes a discontinuous change. For a well diameter slightly larger than any one of these cut-off values, the chain initially collapses to an energy state above the ground state and then undergoes a separate low temperature transition to the ground state. There is a large specific heat peak associated with this latter transition which grows in height as the cut-off diameter is approached and abruptly vanishes at the cut-off diameter itself. Thus, the collapse behavior of short square-well chains is not a smooth function of well diameter. We discuss the implications of this finding for the use of the square-well chain model to study the polymer collapse transition.
No benefit from microcrystalline silicon N layers in single junction amorphous silicon p-i-n solar cells
Authors: Poissant Y. , Chatterjee P. , Roca i Cabarrocas P.
Published: December 2002

The use of phosphorous-doped microcrystalline silicon (μc-Si:H) as the n-type electrode in single junction hydrogenated amorphous silicon solar cells has been studied both experimentally and through computer modeling. The aim is to understand why, in spite of a considerable decrease in the activation energy of the n layer—from 0.2 eV in n-a-Si:H to 0.03 eV in n-μc-Si:H—the open-circuit voltage of solar cells fabricated using these two types of n layer remains almost unchanged. Experimental determination of the work function of n-μc-Si:H and n-a-Si:H by the “flatband heterojunction” technique, has revealed that n-μc-Si:H has a higher electron affinity. Thus, in spite of the fact that the difference in activation energy is 0.17 eV, the difference in built-in potential between the two types of cells reduces to about half. Moreover, modeling of the output characteristics of solar cells, having these two types of N layer, indicates a sharp localization of the field at the N/I interface for the cell with a μc-Si:H N layer. As a consequence, the field in the bulk of the intrinsic layer and, hence, the open-circuit voltage for the two types of cell, remain unchanged.
Wetting of nanopatterned surfaces: The striped surface
Authors: Schneemilch M. , Quirke N. , Henderson J. R.
Published: December 2002

We report an extensive set of results for the wetting of striped nanopatterned surfaces by simple fluids. Metropolis Monte Carlo simulations are used to investigate the validity of Cassie’s law for the surface tension of heterogeneous surfaces, for the case where the surface properties vary periodically on a nanometre scale. A variety of statistical mechanical sum rules is employed to measure the interfacial free energies and a set of interfacial order parameters associated with patterned inhomogeneous fluids. We directly observe two classes of interfacial phase transitions: (i) an unbending transition at the solid–vapor interface, which must precede complete wetting in systems where low-energy regions are not completely wet; (ii) a surface crystallization–layering transition associated with a hemicylindrical region of enhanced liquid structure at the substrate–liquid boundary. For a vapor phase in contact with a striped surface we observe hemicylindrical drops pinned to the stripe boundaries, with a mechanical contact angle unrelated to that defined by Young’s equation. The magnitude and variation of the mechanical contact angle with system parameters can be understood from minimal models of adsorption on patterned surfaces.
Dissociation and evolution of threading dislocations in epitaxial Ba0.3Sr0.7TiO3 thin films grown on (001) LaAlO3
Authors: Lu C. J. , Bendersky L. A. , Chang K. , Takeuchi I.
Published: December 2002

The defect structure of a 350-nm-thick epitaxial Ba0.3Sr0.7TiO3 (BSTO) film grown on (001) LaAlO3 has been investigated using conventional and high-resolution transmission electron microscopy. The dominant defects in the film are edge-type threading dislocations (TDs) with Burgers vectors b=〈100〉 and 〈110〉. Pure-screw TDs and partial TDs of mixed character were also observed. A rapid reduction of defect density occurred after the growth of the first 100 nm BSTO adjacent to the interface. In the top layer of the film, all TDs with b=〈100〉 are perfect while those with b=〈110〉 are usually dissociated into two partials with a small separation (a few nanometers). However, in the near-interface layer of the film, many TDs with b=〈100〉 are split into two or three partials. A high density of extended stacking faults with displacement vectors of 12〈110〉 type were observed. The stacking faults are associated with dissociated dislocations and partial half loops. The mechanisms for the generation, dissociation and evolution of the TDs are discussed.
Theoretical investigation of the temperature dependence of the O+O2 exchange reaction
Authors: Fleurat-Lessard Paul , Grebenshchikov Sergy Yu. , Siebert Rüdiger , Schinke Reinhard , Halberstadt Nadine
Published: December 2002

The exchange reaction O16+18O2→16O18O+18O and, in particular, its dependence on the transition state region is investigated by classical trajectories on three potential energy surfaces, all based on high-level electronic structure calculations. The first one is the original potential recently constructed by Siebert, Schinke, and Bittererová [Phys. Chem. Chem. Phys. 3, 1795 (2001)]; it has a very small barrier above the O+O2 asymptote. The second potential is a modification of the first one in that the transition state region is adjusted according to new electronic structure calculations on higher levels of theory; it has a small barrier below the asymptote. The third potential is obtained by artificially removing this barrier. The variation of the exchange reaction cross section with collision energy and the magnitude of the thermal rate constant at and below room temperature depend drastically on the shape of the potential at intermediate distances. The second potential, which is believed to represent the transition state structure of the true ground-state potential of ozone best, yields a reaction rate for room temperature that is about a factor of three smaller than the experimental rate. The neglect of nonadiabatic transitions between the several electronic states in the entrance channel may explain this discrepancy. The very slight negative temperature dependence found in the calculations is caused by the strong decrease of the reaction cross section with the initial rotational excitation of the oxygen molecule. Statistical calculations give poor agreement with the classical energy and initial-state dependent cross sections. Nevertheless, the statistical thermal rates are in fair agreement with the classical ones, because the overestimation of the cross sections for low j’s and the underestimation for high j’s partly compensate.
Electronic and photophysical properties of C60Cl24
Authors: Coheur P. F. , Liévin J. , Colin R. , Razbirin B.
Published: December 2002

This work examines, by using quantum-chemical calculations, the electronic and optical properties of three highly symmetrical isomers of the C60Cl24 halogenofullerene. The ground state properties of these derivatives are calculated using the semi-empirical Hartree–Fock AM1 approach and discussed in terms of symmetry, charge distribution and electronic conjugation on the fullerene cage. Starting from the optimized geometry, the optical absorption spectrum of each molecule is calculated at the semi-empirical Hartree–Fock INDO/S level, using a large configuration interaction scheme. The results are compared to a visible and near-infrared absorption spectrum of C60Cl24, recorded in solid matrices, at low temperature. From the comparison, it is concluded that a D2h C60Cl24 isomer is responsible for the spectrum observed. The spectrum is analyzed in terms of electronic singlet transitions.
Relativistic effects on the nuclear magnetic shielding tensor
Authors: Melo J. I. , Ruiz de Azua M. C. , Giribet C. G. , Aucar G. A. , Romero R. H.
Published: December 2002

A new approach for calculating relativistic corrections to the nuclear magnetic shieldings is presented. Starting from a full relativistic second order perturbation theory expression a two-component formalism is constructed by transforming matrix elements using the elimination of small component scheme and separating out the contributions from the no-virtual pair and the virtual pair part of the second order corrections to the energy. In this way we avoid a strong simplification used previously in the literature. We arrive at final expressions for the relativistic corrections which are equivalent to those of Fukui et al. [J. Chem Phys. 105, 3175 (1996)] and at some other additional terms correcting both the paramagnetic and the diamagnetic part of the nuclear magnetic shielding. Results for some relativistic corrections to the shieldings of the heavy and light nuclei in HX and CH3X (X=Br,I) at both random phase and second order polarization propagator approach levels are given.
Radio frequency magnetron sputtering deposition of calcium phosphate coatings: Monte Carlo simulations of the deposition process and depositions through an aperture
Authors: Feddes B. , Wolke J. G. C. , Jansen J. A. , Vredenberg A. M.
Published: December 2002

Radio frequency magnetron sputtering deposited calcium phosphate (CaP) coatings can be applied to improve the biological performance of medical implants. However, the deposition process is rather complex. Particle ejection from the sputtering target, particle collisions with the background gas, charge state of the sputtered particles, and resputtering of the deposited film all influence the composition and structure of the film. In this work we study the deposition process of the coatings by performing depositions through an aperture. Thus an image of the sputtering target is obtained. In order to interpret these images, the deposition process is simulated using a Monte Carlo computer simulation. We found that the experimental images obtained at different gas pressures are well predicted by the simulations. The calcium and phosphorus are proven to be ejected as neutrals from the target. The particle ejection distribution could not unambiguously be derived. This was partially because the image is distorted due to resputtering of the deposited film. The resputtering is the result of bombardment by energetic argon from the plasma, or energetic negative oxygen from the target. Phosphorus is preferentially resputtered from the film. In conclusion, we found that depositions with an aperture in combination with Monte Carlo simulations are a powerful combination to study and better understand the deposition process.
Effect of curvature and twist on the conformations of a fluctuating ribbon
Authors: Kessler David A. , Rabin Y.
Published: December 2002

We study the effects of asymmetric bending and twist rigidities and of spontaneous curvature and twist, on the statistical mechanics of fluctuating ribbons. Using a combination of Monte Carlo and differential geometry methods we perform computer simulations and calculate the probability density of the end-to-end distance of a ribbon. We find that for rectilinear ribbons of asymmetric cross section and for spontaneously curved rods with circular cross section, the distribution of end-to-end distance (but not its mean square) is affected by twist rigidity and by spontaneous twist. Possible relevance of these effects to the physics of DNA is discussed.
Physical limit of stability in supercooled D2O and D2O+H2O mixtures
Authors: Kiselev S. B. , Ely J. F.
Published: December 2002

The fluctuation theory of homogeneous nucleation was applied for calculating the physical boundary of metastable states, the kinetic spinodal, in supercooled D2O and D2O+H2O mixtures. The kinetic spinodal in our approach is completely determined by the surface tension and equation of state of the supercooled liquid. We developed a crossover equation of state for supercooled D2O, which predicts a second critical point of low density water–high density water equilibrium, CP2, and represents all available experimental data in supercooled D2O within experimental accuracy. Using Turnbull’s expression for the surface tension we calculated with the crossover equation of state for supercooled D2O the kinetic spinodal, TKS, which lies below the homogeneous nucleation temperature, TH. We show that CP2 always lies inside in the so-called “nonthermodynamic habitat” and physically does not exist. However, the concept of a second “virtual” critical point is physical and very useful. Using this concept we have extended this approach to supercooled D2O+H2O mixtures. As an example, we consider here an equimolar D2O+H2O mixture in normal and supercooled states at atmospheric pressure, P=0.1 MPa.
Qualitative modeling of silica plasma etching using neural network
Authors: Kim Byungwhan , Kwon Kwang Ho
Published: December 2002

An etching of silica thin film is qualitatively modeled by using a neural network. The process was characterized by a 23 full factorial experiment plus one center point, in which the experimental factors and ranges include 100–800 W radio-frequency source power, 100–400 W bias power and gas flow rate ratio CHF3/CF4. The gas flow rate ratio varied from 0.2 to 5.0. The backpropagation neural network (BPNN) was trained on nine experiments and tested on six experiments, not pertaining to the original training data. The prediction ability of the BPNN was optimized as a function of the training parameters. Prediction errors are 180 Å/min and 1.33, for the etch rate and anisotropy models, respectively. Physical etch mechanisms were estimated from the three-dimensional plots generated from the optimized models. Predicted response surfaces were consistent with experimentally measured etch data. The dc bias was correlated to the etch responses to evaluate its contribution. Both the source power (plasma density) and bias power (ion directionality) strongly affected the etch rate. The source power was the most influential factor for the etch rate. A conflicting effect between the source and bias powers was noticed with respect to the anisotropy. The dc bias played an important role in understanding or separating physical etch mechanisms.
First-passage time distribution and non-Markovian diffusion dynamics of protein folding
Authors: Lee Chi-Lun , Stell George , Wang Jin
Published: December 2002

We study the kinetics of protein folding via statistical energy landscape theory. We concentrate on the local-connectivity case, where the configurational changes can only occur among neighboring states, with the folding progress described in terms of an order parameter given by the fraction of native conformations. The non-Markovian diffusion dynamics is analyzed in detail and an expression for the mean first-passage time (MFPT) from non-native unfolded states to native folded state is obtained. It was found that the MFPT has a V-shaped dependence on the temperature. We also find that the MFPT is shortened as one increases the gap between the energy of the native and average non-native folded states relative to the fluctuations of the energy landscape. The second- and higher-order moments are studied to infer the first-passage time distribution. At high temperature, the distribution becomes close to a Poisson distribution, while at low temperatures the distribution becomes a Lévy-type distribution with power-law tails, indicating a nonself-averaging intermittent behavior of folding dynamics. We note the likely relevance of this result to single-molecule dynamics experiments, where a power law (Lévy) distribution of the relaxation time of the underlined protein energy landscape is observed.
Comprehensive description of the dynamical screening of the internal electric fields of AlGaN/GaN quantum wells in time-resolved photoluminescence experiments
Authors: Reale Andrea , Massari Gianluca , Di Carlo Aldo , Lugli Paolo , Vinattieri Anna , Alderighi Daniel , Colocci Marcelo , Semond F. , Grandjean N. , Massies J.
Published: December 2002

We present a combined theoretical and experimental analysis to describe the interplay between polarization field, charge screening, and radiative and nonradiative recombinations in AlGaN/GaN-based nanostructures. We perform the study of photoluminescence (PL) in both stationary and time-resolved PL (TR-PL) conditions, considering also the effect of temperature on the different recombination mechanisms, and especially on nonradiative recombinations. The theoretical analysis is obtained by coupling a complete self-consistent solution of Schrödinger and Poisson equations to determine the electronic states in the nanostructure with a rate equation model to account for time-dependent effects of charge rearrangement. We review the topic of polarization field screening taking into account the most recent results on the evaluation of the very strong coefficients for spontaneous and piezoelectric polarizations that have recently been predicted for III–V nitride semiconductors with natural wurtzite symmetry, and we show how the screening influences both static and dynamic recombination mechanisms. Experimental results are obtained for high-quality GaN/AlGaN multiple quantum wells by means of both continuous-wave (cw) and TR-PL techniques. The case of single quantum well is also considered. The PL measured decays show a time dependence that is not only controlled by radiative lifetimes, which depend on the fields inside the GaN wells, but also on the carrier recombinations through nonradiative channels. We demonstrate that PL emission is influenced by charge accumulation in the well, and a loss of carriers from the ground level induced by an interplay between radiative and nonradiative recombination processes. Moreover, from the analysis of the temperature dependence of the TR-PL decays, we deduce important confirmations of a thermally activated detrapping mechanism that strongly affects the nonradiative recombination processes.
Atomic layer deposition of thin hafnium oxide films using a carbon free precursor
Authors: Conley J. F. , Ono Y. , Tweet D. J. , Zhuang W. , Solanki R.
Published: December 2002

Thin HfO2 films have been deposited on silicon via atomic layer deposition using anhydrous hafnium nitrate [Hf(NO3)4]. Properties of these films have been investigated using x-ray diffraction, x-ray reflectivity, spectroscopic ellipsometry, atomic force microscopy, x-ray photoelectron spectroscopy, and capacitance versus voltage measurements. Smooth and uniform initiation of film growth has been detected on H-terminated silicon surfaces. As-deposited films were amorphous, oxygen rich, and contained residual NO3 and NO2 moieties from the nitrate precursor. Residual nitrates were desorbed by anneals >400 °C, however, the films remained oxygen rich. Crystallization of thin films (<10 nm) occurred at roughly 700 °C. For films less than ∼10 nm thick, the effective dielectric constant of the film and any interfacial layer (neglecting quantum effects) was found to be in the range of k∼10−11. From a plot of electrical thickness versus optical thickness, the dielectric constant of the HfO2 layer was estimated to be kHfO2∼12−14. Leakage current was lower than that of SiO2 films of comparable equivalent thickness. The lower than expected dielectric constant of the film stack is due in part to the presence of an interfacial layer (likely HfSiOx). Excess oxygen in the films may also play a role in the reduced dielectric constant of the HfO2 layer.