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

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

Abnormal inventory and performance in manufacturing companies: evidence from the trade credit channel

This paper examines the value of abnormal inventory and the channels through which firms decrease abnormally high inventory or increase abnormally low inventory for a sample of 976 United Kingdom (UK) manufacturing firms over the period from 2006 to 2015. Using GMM regressions, the results show that (i) an optimal inventory policy exists; and (ii) firms that are able to converge at this optimal inventory level byeither decreasing abnormally high inventory or increasing abnormally low inventory to improve operational and stock performance. Importantly, the results show that trade receivables and trade payables are the channels through which firms achieve efficient inventory management

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

Generating haptic texture using solid noise

Texture enhances haptic interaction by providing unique, distinguishable, and versatile surfaces. In computer haptics, texture can render environments more realistic and provide useful information. In this paper, an algorithm is proposed for virtual texture simulation by using solid noise, where only a few parameters need to be altered to generate a range of realistic and diverse textures by reproducing different frequencies similar to that of real vibrational signals in a virtual environment. The proposed method can capture the textural effect in a haptic simulation while retaining a simple overall geometry and stable update rate. This method also allows the user to change the texture at runtime and can be easily incorporated into any existing code and used in any traditional haptic device without affecting overall haptic-rendering performance. Moreover, the solid noise texture is independent of object geometry and can be applied to any shape without additional computations. We conducted a human-subject study to evaluate the recognition accuracy for each generated haptic texture as well as its realism and correspondence to real texture. The results indicated the high performance of the method and its ability to generate haptic textures with a very high recognition rate that were highly realistic. 2021 The AuthorsThis paper was jointly supported by Qatar University M-QJRC-2020-7. The findings achieved herein are solely the responsibility of the authors. The Open Access funding is provided by the Qatar National Library .Scopu

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

Labor induction with oxytocin in pregnant rats is not associated with oxidative stress in the fetal brain

Despite the widespread use of oxytocin for induction of labor, mechanistic insights into fetal/neonatal wellbeing are lacking because of the absence of an animal model that recapitulates modern obstetric practice. Here, we create and validate a hi-fidelity pregnant rat model that mirrors labor induction with oxytocin in laboring women. The model consists of an implantable preprogrammed microprocessor-controlled infusion pump that delivers a gradually escalating dose of intravenous oxytocin to induce birth at term gestation. We validated the model with molecular biological experiments on the uterine myometrium and telemetry-supported assessment of changes in intrauterine pressure. Finally, we applied this model to test the hypothesis that labor induction with oxytocin would be associated with oxidative stress in the newborn brain. Analysis of biomarkers of oxidative stress and changes in the expression of associated genes were no different between oxytocin-exposed and saline-treated pups, suggesting that oxytocin-induced labor was not associated with oxidative stress in the developing brain. Collectively, we provide a viable and realistic animal model for labor induction and augmentation with oxytocin that would enable new lines of investigation related to the impact of perinatal oxytocin exposure on the mother-infant dyad