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1.
J Laryngol Otol ; 136(9): 809-822, 2022 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-35611844

RESUMO

BACKGROUND: Superior semi-circular canal dehiscence syndrome is a disorder characterised by auditory and vestibular symptoms that can significantly impact quality of life, and yet it has no disease-specific quality of life instrument. METHOD: Thirty-six patients who underwent transmastoid superior semicircular canal resurfacing and plugging were included from an initial cohort of 60 surgically managed patients. A sub-cohort of 19 consecutive patients completed validated symptom and quality of life questionnaires before and after surgery. Of the 36 patients, 31 participated in a telephone semi-structured interview post-operatively. RESULTS: Following surgery, there was a statistically significant improvement in autophony index score (p = 0.02), symptom severity score (p < 0.001) and sound hypersensitivity (p = 0.01). Thematic analysis of telephone interviews suggested three main symptom themes: auditory hypersensitivity, dysequilibrium, headache and concentration difficulties. Dysequilibrium was found to persist post-operatively. CONCLUSION: Surgery improves overall symptoms and quality of life. However, important symptom themes may be overlooked using the outcome measures that are currently available. A unified disease-specific outcome measure is urgently required to better understand the impact of symptoms and measure treatment effects.


Assuntos
Procedimentos Cirúrgicos Otológicos , Humanos , Qualidade de Vida , Estudos Retrospectivos , Canais Semicirculares/cirurgia , Síndrome
2.
Rhinology ; 58(4): 306-313, 2020 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-32452470

RESUMO

BACKGROUND: Throat packs are placed around the airway in patients undergoing upper airway surgical procedures under general anaesthetic to prevent aspiration or ingestion of blood, and consequent chest infections or postoperative nausea and vomiting (PONV). There is no definitive evidence for this, and each time a pack is placed, it risks being retained and obstructing the upper airway. This study aimed to determine whether throat packs are of benefit to patients undergoing upper airway surgical procedures. METHODS: Medline, Embase and Central were searched from conception to 15th January 2018 using individualised search strategies. A systematic search of multiple databases was undertaken using custom strategies to identify all relevant randomised controlled trials. Screening, risk of bias assessment and data extraction were undertaken independently by two authors. Primary outcomes included throat pain and PONV. Secondary outcomes included any adverse event documented. RESULTS: Thirteen papers were eligible for inclusion. No studies reported any instances of retained throat packs. Ten studies assessed the effect of throat packs on post-operative throat pain, with four papers showing a significantly higher incidence of pain when throat packs were used. One study showed throat pain to be slightly, but significantly, worse 24 hours post-surgery when a pack was not used. No paper showed throat packs to be of benefit in preventing PONV. CONCLUSION: The study was limited by methodological flaws of included trials, overall relatively low numbers of patients and difficulty in contacting authors to clarify information and obtain raw data. However, this systematic review found no evidence to support the use of throat packs. This supports the proposal that there is no indication for the routine use of throat packs in ENT, maxillofacial and dental procedures.


Assuntos
Procedimentos Cirúrgicos Bucais , Faringe , Náusea e Vômito Pós-Operatórios , Anestesia , Humanos , Nariz , Dor Pós-Operatória , Náusea e Vômito Pós-Operatórios/prevenção & controle
3.
J Laryngol Otol ; 133(2): 110-114, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30706841

RESUMO

OBJECTIVE: Adenotonsillectomy is frequently performed for obstructive sleep apnoea, but is associated with post-operative respiratory morbidity. This study assessed the effect of paediatric Otrivine (0.05 per cent xylometazoline hydrochloride) on post-operative respiratory compromise. METHODS: Paediatric patients undergoing adenotonsillectomy for obstructive sleep apnoea were included. The control group (n = 24) received no intervention and the intervention group (n = 25) received intra-operative paediatric Otrivine during induction using a nasal patty. Post-operative outcomes included pain, respiratory distress signs and medical intervention level required (simple, intermediate and major). RESULTS: Post-operative respiratory distress signs were exhibited by 4 per cent of the Otrivine group and 21 per cent of the control group. Sixty-eight per cent of the Otrivine group required simple medical interventions post-operatively, compared to 42 per cent of the control group. In the Otrivine group, 4 per cent required intermediate interventions; none required major interventions. In the control group, 12.5 per cent required both intermediate and major interventions. Fifty per cent of the control group reported pain post-operatively, compared with 40 per cent in the Otrivine group. CONCLUSION: Intra-operative paediatric Otrivine may reduce post-operative respiratory compromise in paediatric patients undergoing adenotonsillectomy for obstructive sleep apnoea. A randomised controlled trial is required.


Assuntos
Adenoidectomia/efeitos adversos , Descongestionantes Nasais/administração & dosagem , Cuidados Pós-Operatórios/métodos , Complicações Pós-Operatórias , Apneia Obstrutiva do Sono/tratamento farmacológico , Tonsilectomia/efeitos adversos , Pré-Escolar , Feminino , Humanos , Lactente , Masculino , Projetos Piloto , Polissonografia , Apneia Obstrutiva do Sono/etiologia , Apneia Obstrutiva do Sono/fisiopatologia
4.
J Intensive Care Soc ; 19(4): 351-353, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30505346

RESUMO

BACKGROUND: Leptospirosis is a rare infectious illness caused by the Spirochaete Leptospira. It has a wide-varying spectrum of presentation. We present a rare case of severe cardiogenic shock secondary to leptospirosis, in the absence of its common clinical features. CASE PRESENTATION: A 36-year-old woman presented to our unit with severe cardiogenic shock and subsequent multi-organ failure. Her clinical course was characterised by ongoing pyrexia of unknown origin with concurrent cardiac failure. She was initially managed with broad-spectrum antibiotics and inotropes. Percutaneous cardiac biopsy excluded major causes of myocarditis. On day 21 after presentation, she was found to be IgM-positive for leptospirosis. CONCLUSIONS: This is a rare case of severe cardiogenic shock secondary to leptospirosis infection. The case also highlights the importance of obtaining a thorough social history when assessing a patient with an unusual presentation, as clues can often be missed.

5.
Clin Otolaryngol ; 43(5): 1201-1208, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-29706016

RESUMO

OBJECTIVE: The aim of the study was to perform a systematic review of existing evidence on the role of local anaesthetic nerve block (LAB) in patients undergoing endoscopic sinus surgery (ESS). DESIGN: The databases searched were the Cochrane Register of Controlled Trials, MEDLINE and Embase using the Ovid portal (1946-2017). RESULTS: Seven randomised controlled trials were included. Due to considerable heterogeneity of data, only two studies were pooled into meta-analysis which demonstrated a statistically significantly better surgical field quality during ESS in the LAB group compared with the control group (MD -0.86; 95% CI -2.24, 0.51; P = .009). No adverse events related to LAB toxicity were reported. CONCLUSIONS: Sphenopalatine ganglion LAB with adrenaline carries relatively low risk of morbidity, but may improve the quality of the surgical field in terms of bleeding. However, there are limitations of the study due to heterogeneity of methods, quality and size of the studies. Well-conducted large RCTs are needed using standardised inclusion criteria, balanced baseline characteristics of cohorts, and validated subjective and objective outcome measures.


Assuntos
Anestésicos Locais/uso terapêutico , Endoscopia , Bloqueio Nervoso , Rinite/cirurgia , Sinusite/cirurgia , Humanos
6.
J Endocrinol Invest ; 41(1): 33-47, 2018 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-28643299

RESUMO

BACKGROUND AND OBJECTIVE: Fetuin-A is a liver-derived circulating protein that is associated with insulin resistance and diabetes. The objective of this systematic review and meta-analysis of published observational studies was to investigate mean levels of fetuin-A in T2D patients and the relationship between blood fetuin-A levels and T2D risk. MATERIALS AND METHODS: PubMed, Embase, Google Scholar, Web of Science, and The Cochrane Library were systematically searched for potential relevant studies up to 1 December 2016. Natural logarithm-transformed estimate risks, standard mean differences on the basis of Hedges's adjusted g, and 95% confidence intervals (CIs) were calculated for all eligible studies and were combined to measure the pooled data using random-effects model. RESULTS: A total of 32 studies including 27 case-control and 5 cohort studies were included in the current study. Fetuin-A levels in T2D patients were significantly higher than control groups [Hedges' g = 1.73, 95% CI (1.25-2.22), P < 0.001], with significant heterogeneity across studies (P < 0.001, I 2 = 98.46%). Findings from meta-analyses of cohort studies showed a statistically significant association between fetuin-A levels and T2D risk [rate ratio = 1.62, 95% CI (1.26-2.08), P < 0.001], with no significant heterogeneity (P = 0.10, I 2 = 46.06%). CONCLUSION: We found a significant relationship between the fetuin-A levels with T2D risk. Although fetuin-A may be as a potential screening and prediction biomarker or a therapeutic target in T2D patients, further studies are required in this regard.


Assuntos
Diabetes Mellitus Tipo 2/sangue , alfa-2-Glicoproteína-HS/metabolismo , Biomarcadores/sangue , Estudos de Casos e Controles , Humanos , Resistência à Insulina , Fatores de Risco
7.
Case Rep Surg ; 2018: 9659232, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30652046

RESUMO

Minimal access surgery is increasingly popular to reduce postoperative morbidity and enhance recovery. We present a case of a patient who underwent bilateral minimally invasive thoracic and cardiac surgery. An 81-year-old woman was diagnosed with T1aN0M0 left upper lobe small-cell lung cancer and underwent single-port left video-assisted thoracoscopic surgery (VATS) upper lobectomy in 2016. She developed a contralateral right lower lobe nodule and underwent a single-port right VATS wedge resection of the lower lobe nodule, subsequently confirmed as necrotising granulomatous inflammation with acid-fast bacilli, consistent with previous tuberculosis (TB) infection. On postoperative day 1, she had an episode of self-reverting ventricular tachycardia and bradycardia. Subsequent myocardial perfusion scan and coronary angiogram showed significant LV dysfunction and severe coronary artery disease with a left main stem (LMS) lesion. After agreement at MDT, an Endo-ACAB (endoscopic atraumatic coronary artery bypass grafting) was performed, via 3 ports, with the left internal mammary artery anastomosed to left anterior descending artery. She recovered well postoperatively and was discharged. Multiple sequential minimally invasive procedures are now routine and can be performed safely in patients with a complex combination of pathologies. In this case, bilateral single-port (anatomic and nonanatomic) lung resections were undertaken followed by coronary revascularisation with a total of 5 minimal access ports.

8.
Horm Metab Res ; 48(7): 417-26, 2016 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-27311126

RESUMO

Cardiovascular disease (CVD) has become a concerning health problem because of its increasing prevalence. Vegetable oils such as rice bran oil may improve blood lipids, risk factors for CVD. We performed a systematic review and meta-analysis to identify and quantify the effects of rice bran oil on lipid profiles in humans. Literature databases (Pubmed, Scopus, Science Direct, Proquest, Ovid, and Google Scholar) were systematically searched until the end of November 2015, with no restrictions regarding study design, time, or language. The variables extracted for the meta-analysis included low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), total cholesterol (TC), triacylglycerol (TAG), VLDL-C, apoA, apoB, Lp(a), TC/HDL-C, and LDL-C/HDL-C. From 415 identified articles, 11 randomized controlled trials met the eligibility criteria and were included in our review. Rice bran oil consumption resulted in a significant decrease in concentrations of LDL-C (-6.91 mg/dl, 95% CI, -10.24 to -3.57; p<0.001) and TC (-12.65 mg/dl; 95% CI, -18.04 to -7.27; p<0.001). The increase in HDL-C levels were considerable only in men (6.65 mg/dl; 95% CI, 2.38-10.92; p=0.002). Results of our meta-analysis provided no evidence of a significant effekt of rice bran oil on other lipid profile components. In conclusion, consumption of rice bran oil can reduce LDL-C and TC concentrations, which may lead to prevention and control of CVD. It also has favorable effects on HDL-C concentrations in men. However, changes related to other lipid profile components are not considerable.


Assuntos
LDL-Colesterol/sangue , Óleos de Plantas/uso terapêutico , Ensaios Clínicos Controlados Aleatórios como Assunto , HDL-Colesterol/sangue , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Óleo de Farelo de Arroz , Triglicerídeos/sangue
9.
J Laryngol Otol ; 130(6): 516-20, 2016 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-27160379

RESUMO

BACKGROUND: The field of ENT surgery is one of the most varied specialties, with numerous subspecialties and continuing divergence. With this evolution there comes, however, a risk that specialists become de-skilled in certain areas. In the case of ENT emergencies, this can be particularly dangerous. METHODS: Current guidance from relevant UK professional membership bodies regarding emergency surgery provision was inspected and a literature search was performed to identify studies relating to management of ENT emergencies in the context of increasing subspecialisation. RESULTS AND CONCLUSION: The specialty currently has provisions in place to ensure timely, appropriate and safe management of emergencies, in the form of guidelines and emergency clinics; however, there is scope for improvement of the system.


Assuntos
Emergências , Otolaringologia , Otorrinolaringopatias/terapia , Guias de Prática Clínica como Assunto , Qualidade da Assistência à Saúde , Especialização , Gerenciamento Clínico , Humanos , Segurança do Paciente , Sociedades Médicas , Tempo para o Tratamento , Reino Unido
10.
Horm Metab Res ; 48(4): 251-6, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-27065462

RESUMO

Although the effects of dietary glycemic index (GI) on insulin resistance are well documented in adults, the complex interaction among glucose intolerance, inflammatory markers, and adipokine concentration has not been well studied, especially among adolescents. We investigated the effect of a low glycemic index (LGI) diet on insulin concentration, fasting blood sugar (FBS), inflammatory markers, and serum adiponectin concentration among healthy obese/overweight adolescent females. In this parallel randomized clinical trial, 2 different diets, an LGI diet and a healthy nutritional recommendation diet (HNRD) with similar macronutrient composition were prescribed to 50 obese and overweight adolescent girls with the same pubertal status. Biochemical markers FBS, serum insulin concentration, high sensitivity C-reactive protein (hs-CRP), interleukin 6 (IL-6), and adiponectin were measured before and after a 10 week intervention. Using an intention-to-treat analysis, data from 50 subjects were analyzed. According to a dietary assessment, GI in the LGI group was 43.22±0.54. While the mean for FBS, serum insulin concentration, the homeostasis model assessment (HOMA), the quantitative insulin sensitivity check index (QUICKI), and adiponectin concentration did not differ significantly within each group, the average hs-CRP and IL-6 decreased significantly in the LGI diet group after the 10 week intervention (p=0.009 and p=0.001; respectively). Comparing percent changes, we found a marginally significant decrease in hs-CRP in the LGI group compared with the HNRD group after adjusting for confounders. Compliance with an LGI diet may have favorable effect on inflammation among overweight and obese adolescent girls.


Assuntos
Adiponectina/sangue , Mediadores da Inflamação/sangue , Obesidade/dietoterapia , Sobrepeso/dietoterapia , Adolescente , Biomarcadores/sangue , Glicemia/metabolismo , Proteína C-Reativa/metabolismo , Criança , Dieta com Restrição de Carboidratos , Feminino , Índice Glicêmico , Humanos , Insulina/sangue , Interleucina-6/sangue , Obesidade/sangue , Sobrepeso/sangue
11.
Obes Rev ; 15(9): 740-8, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-24815945

RESUMO

A body of literature exists regarding the association of red and processed meats with obesity; however, the nature and extent of this relation has not been clearly established. The aim of this study is to conduct a systematic review and meta-analysis of the relationship between red and processed meat intake and obesity. We searched multiple electronic databases for observational studies on the relationship between red and processed meat intake and obesity published until July 2013. Odds ratios (ORs) and means for obesity-related indices and for variables that may contribute to heterogeneity were calculated. A systematic review and a meta-analysis were conducted with 21 and 18 studies, respectively (n = 1,135,661). The meta-analysis (n = 113,477) showed that consumption of higher quantities of red and processed meats was a risk factor for obesity (OR: 1.37; 95% CI: 1.14-1.64). Pooled mean body mass index (BMI) and waist circumference (WC) trends showed that in comparison to those in the lowest ntile, subjects in the highest ntile of red and processed meat consumption had higher BMI (mean difference: 1.37; 95% CI: 0.90-1.84 for red meat; mean difference: 1.32; 95% CI: 0.64-2.00 for processed meat) and WC (mean difference: 2.79; 95% CI: 1.86-3.70 for red meat; mean difference: 2.77; 95% CI: 1.87-2.66 for processed meat). The current analysis revealed that red and processed meat intake is directly associated with risk of obesity, and higher BMI and WC. However, the heterogeneity among studies is significant. These findings suggest a decrease in red and processed meat intake.


Assuntos
Doença das Coronárias/prevenção & controle , Dieta/efeitos adversos , Produtos da Carne/efeitos adversos , Carne/efeitos adversos , Obesidade/prevenção & controle , Índice de Massa Corporal , Doença das Coronárias/etiologia , Comportamento Alimentar , Humanos , Obesidade/etiologia , Estudos Observacionais como Assunto , Fatores de Risco , Circunferência da Cintura
12.
J Chem Phys ; 137(9): 094707, 2012 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-22957586

RESUMO

We propose a barrierless mechanism for describing the oxidation of Al(111) in which oxygen atoms located on the outer surface extract aluminum atoms of the surface layers through local cooperation of other pre-adsorbed oxygen atoms. We show the details of this complex chemical process that kinetically competes with the non-destructive formation of an oxygen monolayer onto the Al surface, thus elucidating the initial aluminum oxidation regime. We demonstrate that further stripping of the complete surface Al layer is consistent with both (i) the formation of a defective alumina structure and (ii) an oxide capping layer preventing further oxidation at low temperature.

13.
Eur Phys J E Soft Matter ; 35(8): 75, 2012 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-22898937

RESUMO

DNA sequencing using nanopores is closer than ever to become a reality, but further research and development still need to be done, especially to unravel the atomic-scale mechanisms of induced DNA stretching. At this level, molecular modeling and simulation are essential to investigate DNA conformational flexibility and its response to the forces involved. In this work, through a "Static Mode" approach, we present a directed exploration of the deformations of a 27-mer subjected to externally imposed forces, as it could be in a nanopore. We show how the DNA sugar-phosphate backbone undergoes the majority of the induced deformation, before the base pairing is affected, and to what extent unzipping initiation depends on the force direction.


Assuntos
DNA/química , Modelos Moleculares , Estresse Mecânico , Pareamento de Bases , Sequência de Bases , Fenômenos Biomecânicos , DNA/genética , Nanoporos , Fosfatos/química
14.
J Med Eng Technol ; 36(1): 42-9, 2012 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-22149293

RESUMO

This article presents a novel method for diagnosis of valvular heart disease (VHD) based on phonocardiography (PCG) signals. Application of the pattern classification and feature selection and reduction methods in analysing normal and pathological heart sound was investigated. After signal preprocessing using independent component analysis (ICA), 32 features are extracted. Those include carefully selected linear and nonlinear time domain, wavelet and entropy features. By examining different feature selection and feature reduction methods such as principal component analysis (PCA), genetic algorithms (GA), genetic programming (GP) and generalized discriminant analysis (GDA), the four most informative features are extracted. Furthermore, support vector machines (SVM) and neural network classifiers are compared for diagnosis of pathological heart sounds. Three valvular heart diseases are considered: aortic stenosis (AS), mitral stenosis (MS) and mitral regurgitation (MR). An overall accuracy of 99.47% was achieved by proposed algorithm.


Assuntos
Algoritmos , Doenças das Valvas Cardíacas/diagnóstico , Ruídos Cardíacos , Humanos , Fonocardiografia/métodos , Análise de Componente Principal
15.
Phys Chem Chem Phys ; 11(19): 3701-9, 2009 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-19421481

RESUMO

We apply our recently developed approach, combining advanced ab initio density functional theory (DFT) methods with a probabilistic kinetic Monte Carlo (KMC) scheme, to quantify the properties of mesoscopic size systems operating in real experimental conditions. The application concerns the investigation of the atomic layer deposition (ALD) of HfO2 film growth on Si(100) surface. We show that the proposed models offer guidance in the optimization of the experimental deposition processes, in terms of OH density on the substrate, optimal growth temperature, pulse durations, and finally growth kinetics.

16.
Eur Phys J E Soft Matter ; 28(1): 17-25, 2009 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-19139941

RESUMO

We present a new competitive method for the atomic scale treatment of macromolecular flexibility called Static Mode method. This method is based on the "induced-fit" concept, i.e. it maps the intrinsic deformations of a macromolecule subject to diverse external excitations. The algorithm makes it possible to obtain a set of deformations, each one corresponding to a specific interaction on a specific molecular site, in terms of force constants contained in the energy model. In this frame, the docking problem can be expressed in terms of interaction sites between the two molecules, the molecular deformations being extracted from the pre-calculated Static Modes of each molecule. Some preliminary basic examples aimed at illustrating potential applications where macro- or bio-molecular flexibility is of key importance are given: flexibility inducing conformational changes in the case of furanose ring and flexibility for the characterization, including allostery, of poly(N-isopropylacrylamide)(P-NIPAM) active sites. We also discuss how this procedure allows "induced-fit" flexible molecular docking, beyond state-of-the-art semi-rigid methods.


Assuntos
Substâncias Macromoleculares/química , Modelos Moleculares , Resinas Acrílicas/química , Resinas Acrílicas/metabolismo , Algoritmos , Nucleotídeos de Desoxiadenina/química , Nucleotídeos de Desoxiadenina/metabolismo , Ligação de Hidrogênio , Substâncias Macromoleculares/metabolismo , Conformação Molecular , Timidina Monofosfato/química , Timidina Monofosfato/metabolismo
17.
J Chem Theory Comput ; 4(11): 1915-27, 2008 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-26620335

RESUMO

An original integrated approach developed within a multiscale strategy, which combines first-principles quantum simulations and kinetic Monte Carlo (KMC), is presented to investigate the atomic layer deposition (ALD) of HfO2 on Si(100) surface. Density functional theory within the hybrid functional is used to determine the detailed physicochemical mechanisms and associated energetics of the two half cycles taking place during the initial stage of film growth. A kinetic Monte Carlo model is then proposed that deals with the stochastic nature of the calculated DFT mechanisms and barriers. Beyond the chemical information emanating from DFT calculations, the lattice-based KMC approach requires preliminary physical considerations issued from the crystal structures that the system is intended to adopt. This is especially critical in the case of heterogeneous systems like oxides deposited on silicon. We also describe (i) how atomistic configuration changes are performed as a result of local events consisting in elementary reaction mechanisms occurring on specific lattice sites, (ii) the temporal dynamics, governed by transition probabilities, calculated for every event from DFT activation barriers, and (iii) the relation of KMC with the ALD experimental procedure. Some preliminary validation results of the whole multiscale strategy are given for illustration and pertinence with regard of the technological main issues.

18.
J Chem Phys ; 126(11): 114707, 2007 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-17381228

RESUMO

First principles calculations and scanning tunneling microscopy studies of the oxidation of Si(100)-(2x1) surfaces by molecular oxygen reveal that the surface silanone (O)(Si=O) species is remarkably stable, constituting the key intermediate for initial oxidation. The propensity for oxygen to remain within the top surface layer as opposed to incorporating within Si-Si backbonds is surprisingly high. This resistance to incorporation into a cubic lattice even at higher coverages could be a factor to facilitate surface amorphization in subsequent steps.

19.
J Am Chem Soc ; 127(27): 9776-80, 2005 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-15998082

RESUMO

Quantum chemical calculations have been carried out on the grafting of chain organosilane compounds on SiO(2)-hydroxylated solid surfaces. It is shown that a single molecule interacting with the surface lies flat to it, inhibiting further homogeneous film growth. This adsorption exhibits two molecule/surface interactions: a covalent bond on one side of the molecule and a hydrogen bond on the other side. We then investigate the possible preorganization of the molecules before grafting due to the presence of water molecules either in the gas/liquid phase or near the surface. This gives rise to the formation of dimerized chains. We then demonstrate that this preorganization process prevents subsequent lying flat of the molecules to the substrate after grafting. Energetics and associated configurations of the overall deposition process are discussed in detail and provide new insights on the understanding of the formation of self-assembled homogeneous organic films on microelectronics-type substrates.

20.
Phys Rev E Stat Nonlin Soft Matter Phys ; 65(6 Pt 2): 066406, 2002 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-12188834

RESUMO

By using a relativistic fluid model, a nonlinear theory for the propagation of an intense laser pulse in an inhomogeneous cold plasma is developed. Assuming that the radiation spot size is larger than the plasma wavelength, we derive an envelope equation for the momentum of the electron fluid, taking into account relativistic electron mass variation and finite amplitude electron density perturbations that are driven by the relativistic ponderomotive force of light. Localized solutions of the envelope equation are discussed from an energy integral containing an effective potential. Numerical results for envelope solitons are obtained in a quasistationary approximation. The dependency of these localized solutions on the amplitude and the group velocity of the laser pulse is discussed. Also derived is an equation that governs the dynamics of the pulse center.

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