Nonlinear surface plasmons

We derive an asymptotic equation for quasi-static, nonlinear surface plasmons propagating on a planar interface between isotropic media. The plasmons are nondispersive with a constant linearized frequency that is independent of their wavenumber. The spatial profile of a weakly nonlinear plasmon satisfies a nonlocal, cubically nonlinear evolution equation that couples its left-moving and right-moving Fourier components. We prove short-time existence of smooth solutions of the asymptotic equation and describe its Hamiltonian structure. We also prove global existence of weak solutions of a unidirectional reduction of the asymptotic equation. Numerical solutions show that nonlinear effects can lead to the strong spatial focusing of plasmons. Solutions of the unidirectional equation appear to remain smooth when they focus, but it is unclear whether or not focusing can lead to singularity formation in solutions of the bidirectional equation

Maximum entropy models for antibody diversity

Recognition of pathogens relies on families of proteins showing great diversity. Here we construct maximum entropy models of the sequence repertoire, building on recent experiments that provide a nearly exhaustive sampling of the IgM sequences in zebrafish. These models are based solely on pairwise correlations between residue positions, but correctly capture the higher order statistical properties of the repertoire. Exploiting the interpretation of these models as statistical physics problems, we make several predictions for the collective properties of the sequence ensemble: the distribution of sequences obeys Zipf's law, the repertoire decomposes into several clusters, and there is a massive restriction of diversity due to the correlations. These predictions are completely inconsistent with models in which amino acid substitutions are made independently at each site, and are in good agreement with the data. Our results suggest that antibody diversity is not limited by the sequences encoded in the genome, and may reflect rapid adaptation to antigenic challenges. This approach should be applicable to the study of the global properties of other protein families

Statistical mechanics of transcription-factor binding site discovery using Hidden Markov Models

Hidden Markov Models (HMMs) are a commonly used tool for inference of transcription factor (TF) binding sites from DNA sequence data. We exploit the mathematical equivalence between HMMs for TF binding and the "inverse" statistical mechanics of hard rods in a one-dimensional disordered potential to investigate learning in HMMs. We derive analytic expressions for the Fisher information, a commonly employed measure of confidence in learned parameters, in the biologically relevant limit where the density of binding sites is low. We then use techniques from statistical mechanics to derive a scaling principle relating the specificity (binding energy) of a TF to the minimum amount of training data necessary to learn it.Comment: 25 pages, 2 figures, 1 table V2 - typos fixed and new references adde

Satisfaction of patients on chronic haemodialysis and peritoneal dialysis

BACKGROUND: In contrast to quality of life, patient satisfaction on chronic haemodialysis (HD) and peritoneal dialysis (PD) has only rarely been studied. PATIENTS AND METHODS: All chronic HD and PD patients of the 19 centres located in western Switzerland were asked to complete a specific questionnaire, assessing dialysis centre characteristics, treatment modalities, and information received before and during dialysis treatment. Comparison between satisfaction with PD and HD was carried out on the patients in the nine centres offering both treatment modalities. RESULTS: Of the 558 questionnaires distributed to chronic HD patients, 455 were returned (response rate 82%). Fifty of 64 PD patients (78%) returned the questionnaire. The two groups were similar in age, gender, and duration of dialysis treatment. Completion rates were >90% for a majority of questions, with the lowest rate for information on sexuality (49% in HD and 54% in PD respectively). The lowest scores were recorded for information received about complications and costs of dialysis, and impact of end-stage kidney disease on sexuality. Satisfaction was lower in anonymous questionnaires. Satisfaction of PD patients was significantly better in 50% of the questions, particularly session tolerance (p<0.001), information about dialysis sessions (p=0.007), and complications (p=0.006). CONCLUSIONS: PD patients were on average more satisfied with their treatment than HD patients. Satisfaction could be improved with more information about potential adverse treatment effects

Writing melancholy : the death of the intellectual in modern Arabic literature

textIn this study on the depiction of the death of the Arab intellectual in elegiac writings since 1967, I examine the ways in which modern and contemporary Arab writers who identify with different literary and historical generations have mourned and commemorated the death of other Arab intellectuals. Drawing on theoretical contributions from psychoanalysis, poststructuralism, and gender studies, particularly those investigating the articulations of masculinity and femininity in mourning practices, I argue that the psychological and political imprints of loss that emerge in the modern and contemporary elegies, eulogies, novels, and memoirs that I analyze, contribute to an elegiac discourse that is melancholic at its core. Both a somber outlook towards the world and a resistance to complete the work of mourning, melancholia, as I interpret it in my analysis of Arabic elegiac writings, is an emotion experienced collectively and subsequently channeled in the literary text. In their elegiac writings, the poets Mahmoud Darwish (1941-2008), Samih al-Qasem (b. 1939), Mohammad al-Maghout (1934-2006), and the novelist Jabra Ibrahim Jabra (1919-2004), have expressed a collective disillusionment with the modern role Arab intellectual and his embodiment of his generation’s political and ethical sensibilities following the 1967 war. These writers, I argue, understand the death of their peers as a signifier of their generation’s failure to lead their societies to the socialist and nationalist utopias that they have collectivity imagined. I demonstrate how in their elegiac writings, these poets and novelists in fact lament themselves and the collapse of their own modernist intellectual project in which they had attributed to the written word the power of collective salvation. As I investigate the commemoration of the intellectual in contemporary elegiac texts, I explore the works of young writers such as the Lebanese Rabih Jaber (b. 1974) and the Saudi Seba al-Herz (b. circa 1984). By gradually disengaging from the elegiac modes that their precursors had defined in the 1960s and 1970s, the two novelists have formulated counternarratives of mourning. The narrative that emanates from this literary subversion, I contend, presents a distinctive elegiac rhetoric, in which melancholia ceases to be a collective condition, but rather an individual and intimate state of mind of young protagonists marginalized by and critical of the dominant intellectual circles.Middle Eastern Studie

Pioglitazone improves fat distribution, the adipokine profile and hepatic insulin sensitivity in non-diabetic end-stage renal disease subjects on maintenance dialysis: a randomized cross-over pilot study.

BACKGROUND: Fat redistribution, increased inflammation and insulin resistance are prevalent in non-diabetic subjects treated with maintenance dialysis. The aim of this study was to test whether pioglitazone, a powerful insulin sensitizer, alters body fat distribution and adipokine secretion in these subjects and whether it is associated with improved insulin sensitivity. TRIAL DESIGN: This was a double blind cross-over study with 16 weeks of pioglitazone 45 mg vs placebo involving 12 subjects. METHODS: At the end of each phase, body composition (anthropometric measurements, dual energy X-ray absorptometry (DEXA), abdominal CT), hepatic and muscle insulin sensitivity (2-step hyperinsulinemic euglycemic clamp with 2H2-glucose) were measured and fasting blood adipokines and cardiometabolic risk markers were monitored. RESULTS: Four months treatment with pioglitazone had no effect on total body weight or total fat but decreased the visceral/sub-cutaneous adipose tissue ratio by 16% and decreased the leptin/adiponectin (L/A) ratio from 3.63×10-3 to 0.76×10-3. This was associated with a 20% increase in hepatic insulin sensitivity without changes in muscle insulin sensitivity, a 12% increase in HDL cholesterol and a 50% decrease in CRP. CONCLUSIONS/LIMITATIONS: Pioglitazone significantly changes the visceral-subcutaneous fat distribution and plasma L/A ratio in non diabetic subjects on maintenance dialysis. This was associated with improved hepatic insulin sensitivity and a reduction of cardio-metabolic risk markers. Whether these effects may improve the outcome of non diabetic end-stage renal disease subjects on maintenance dialysis still needs further evaluation. TRIAL REGISTRATION: ClinicalTrial.gov NCT01253928

Reactive scattering of H2 from Cu(100): comparison of dynamics calculations based on the specific reaction parameter approach to density functional theory with experiment

We present new experimental and theoretical results for reactive scattering of dihydrogen from Cu(100). In the new experiments, the associative desorption of H2 is studied in a velocity resolved and final rovibrational state selected manner, using time-of-flight techniques in combination with resonance-enhanced multi-photon ionization laser detection. Average desorption energies and rota- tional quadrupole alignment parameters were obtained in this way for a number of (v = 0, 1) ro- tational states, v being the vibrational quantum number. Results of quantum dynamics calculations based on a potential energy surface computed with a specific reaction parameter (SRP) density func- tional, which was derived earlier for dihydrogen interacting with Cu(111), are compared with the results of the new experiments and with the results of previous molecular beam experiments on sticking of H2 and on rovibrationally elastic and inelastic scattering of H2 and D2 from Cu(100). The calculations use the Born-Oppenheimer and static surface approximations. With the functional derived semi-empirically for dihydrogen + Cu(111), a chemically accurate description is obtained of the molecular beam experiments on sticking of H2 on Cu(100), and a highly accurate descrip- tion is obtained of rovibrationally elastic and inelastic scattering of D2 from Cu(100) and of the orientational dependence of the reaction of (v = 1, j = 2 − 4) H2 on Cu(100). This suggests that a SRP density functional derived for H2 interacting with a specific low index face of a metal will yield accurate results for H2 reactively scattering from another low index face of the same metal, and that it may also yield accurate results for H2 interacting with a defected (e.g., stepped) surface of that same metal, in a system of catalytic interest. However, the description that was obtained of the average desorption energies, of rovibrationally elastic and inelastic scattering of H2 from Cu(100), and of the orientational dependence of reaction of (v = 0, j = 3 − 5, 8) H2 on Cu(100) compares less well with the available experiments. More research is needed to establish whether more accurate SRP-density functional theory dynamics results can be obtained for these observables if surface atom motion is added to the dynamical model. The experimentally and theoretically found dependence of the rotational quadrupole alignment parameter on the rotational quantum number provides evidence for rotational enhancement of reaction at low translational energies.Fil: Sementa, L.. Leiden University; Países Bajos. Istituto per i Processi Chimico-Fisici of the Consiglio Nazionale delle Ricerche; ItaliaFil: Wijzenbroek, M.. Leiden University; Países BajosFil: Van Kolck, B. J.. Leiden University; Países BajosFil: Somers, M. F.. Leiden University; Países BajosFil: Al-Halabi, A.. Leiden University; Países BajosFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Olsen, R. A.. Leiden University; Países Bajos. SINTEF Materials and Chemistry; NoruegaFil: Kroes, G. J.. Leiden University; Países BajosFil: Rutkowski, M.. Westfalische Wilhelms Universitat; AlemaniaFil: Thewes, C.. Westfalische Wilhelms Universitat; AlemaniaFil: Kleimeier, N. F.. Westfalische Wilhelms Universitat; AlemaniaFil: Zacharias, H.. Westfalische Wilhelms Universitat; Alemani

Mammography screening: views from women and primary care physicians in Crete

Background: Breast cancer is the most commonly diagnosed cancer among women and a leading cause of death from cancer in women in Europe. Although breast cancer incidence is on the rise worldwide, breast cancer mortality over the past 25 years has been stable or decreasing in some countries and a fall in breast cancer mortality rates in most European countries in the 1990s was reported by several studies, in contrast, in Greece have not reported these favourable trends. In Greece, the age-standardised incidence and mortality rate for breast cancer per 100.000 in 2006 was 81,8 and 21,7 and although it is lower than most other countries in Europe, the fall in breast cancer mortality that observed has not been as great as in other European countries. There is no national strategy for screening in this country. This study reports on the use of mammography among middleaged women in rural Crete and investigates barriers to mammography screening encountered by women and their primary care physicians. Methods: Design: Semi-structured individual interviews. Setting and participants: Thirty women between 45–65 years of age, with a mean age of 54,6 years, and standard deviation 6,8 from rural areas of Crete and 28 qualified primary care physicians, with a mean age of 44,7 years and standard deviation 7,0 serving this rural population. Main outcome measure: Qualitative thematic analysis. Results: Most women identified several reasons for not using mammography. These included poor knowledge of the benefits and indications for mammography screening, fear of pain during the procedure, fear of a serious diagnosis, embarrassment, stress while anticipating the results, cost and lack of physician recommendation. Physicians identified difficulties in scheduling an appointment as one reason women did not use mammography and both women and physicians identified distance from the screening site, transportation problems and the absence of symptoms as reasons for non-use. Conclusion: Women are inhibited from participating in mammography screening in rural Crete. The provision of more accessible screening services may improve this. However physician recommendation is important in overcoming women's inhibitions. Primary care physicians serving rural areas need to be aware of barriers preventing women from attending mammography screening and provide women with information and advice in a sensitive way so women can make informed decisions regarding breast caner screening