96 research outputs found
Casimir and van der Waals force between two plates or a sphere (lens) above a plate made of real metals
The Casimir and van der Waals forces acting between two metallic plates or a
sphere (lens) above a plate are calculated accounting for the finite
conductivity of the metals. The simple formalism of surface modes is briefly
presented which allows the possibility to obtain the generalization of Lifshitz
results for the case of two semi-spaces covered by the thin layers. Additional
clarifications of the regularization procedure provides the means to obtain
reliable results not only for the force but also for the energy density. This,
in turn, leads to the value of the force for the configuration of a sphere
(lens) above a plate both of which are covered by additional layers. The
Casimir interaction between Al and Au test bodies is recalculated using the
optical tabulated data for the complex refractive index of these metals. The
computations turn out to be in agreement with the perturbation theory up to the
fourth order in relative penetration depth of electromagnetic zero point
oscillations into the metal. The disagreements between the results recently
presented in the literature are resolved. The Casimir force between Al bodies
covered by the thin Au layers is computed and the possibility to neglect
spatial dispersion effects is discussed as a function the layer thickness. The
van der Waals force is calculated including the transition region to the
Casimir force. The pure non-retarded van der Waals force law between Al and Au
bodies is shown to be restricted to a very narrow distance interval from 0.5 nm
to (2--4) nm. New, more exact, values of the Hamaker constant for Al and Au are
determined.Comment: 5 figure
Medical studentsβ preparedness for professional activities in early clerkships
Background Sufficient preparedness is important for transitions to workplace
participation and learning in clinical settings. This study aims to analyse
medical studentsβ preparedness for early clerkships using a three-dimensional,
socio-cognitive, theory-based model of preparedness anchored in specific
professional activities and their supervision level. Methods Medical students
from a competency-based undergraduate curriculum were surveyed about
preparedness for 21 professional activities and level of perceived supervision
during their early clerkships via an online questionnaire. Preparedness was
operationalized by the three dimensions of confidence to carry out clerkship
activities, being prepared through university teaching and coping with failure
by seeking support. Factors influencing preparedness and perceived stress as
outcomes were analysed through step-wise regression. Results Professional
activities carried out by the students (n = 147; 19.0%) and their supervision
levels varied. While most students reported high confidence to perform the
tasks, the activity-specific analysis revealed important gaps in preparation
through university teaching. Students regularly searched for support in case
of difficulty. One quarter of the variance of each preparedness dimension was
explained by self-efficacy, supervision quality, amount of prior clerkship
experience and nature of professional activities. Preparedness contributed to
predicting perceived stress. Conclusions The applied three-dimensional concept
of preparedness and the task-specific approach provided a detailed and
meaningful view on medical studentsβ workplace participation and experiences
in early clerkships
Assessing the Quality of Clinical Teachers: A Systematic Review of Content and Quality of Questionnaires for Assessing Clinical Teachers
BACKGROUND: Learning in a clinical environment differs from formal educational settings and provides specific challenges for clinicians who are teachers. Instruments that reflect these challenges are needed to identify the strengths and weaknesses of clinical teachers. OBJECTIVE: To systematically review the content, validity, and aims of questionnaires used to assess clinical teachers. DATA SOURCES: MEDLINE, EMBASE, PsycINFO and ERIC from 1976 up to March 2010. REVIEW METHODS: The searches revealed 54 papers on 32 instruments. Data from these papers were documented by independent researchers, using a structured format that included content of the instrument, validation methods, aims of the instrument, and its setting. Results : Aspects covered by the instruments predominantly concerned the use of teaching strategies (included in 30 instruments), supporter role (29), role modeling (27), and feedback (26). Providing opportunities for clinical learning activities was included in 13 instruments. Most studies referred to literature on good clinical teaching, although they failed to provide a clear description of what constitutes a good clinical teacher. Instrument length varied from 1 to 58 items. Except for two instruments, all had to be completed by clerks/residents. Instruments served to provide formative feedback ( instruments) but were also used for resource allocation, promotion, and annual performance review (14 instruments). All but two studies reported on internal consistency and/or reliability; other aspects of validity were examined less frequently. CONCLUSIONS: No instrument covered all relevant aspects of clinical teaching comprehensively. Validation of the instruments was often limited to assessment of internal consistency and reliability. Available instruments for assessing clinical teachers should be used carefully, especially for consequential decisions. There is a need for more valid comprehensive instruments
Heterozygous missense variants of LMX1A lead to nonsyndromic hearing impairment and vestibular dysfunction
Unraveling the causes and pathomechanisms of progressive disorders is essential for the development of therapeutic strategies. Here, we identified heterozygous pathogenic missense variants of LMX1A in two families of Dutch origin with progressive nonsyndromic hearing impairment (HI), using whole exome sequencing. One variant, c.721G > C (p.Val241Leu), occurred de novo and is predicted to affect the homeodomain of LMX1A, which is essential for DNA binding. The second variant, c.290G > C (p.Cys97Ser), predicted to affect a zinc-binding residue of the second LIM domain that is involved in proteinβprotein interactions. Bi-allelic deleterious variants of Lmx1a are associated with a complex phenotype in mice, including deafness and vestibular defects, due to arrest of inner ear development. Although Lmx1a mouse mutants demonstrate neurological, skeletal, pigmentation and reproductive system abnormalities, no syndromic features were present in the participating subjects of either family. LMX1A has previously been suggested as a candidate gene for intellectual disability, but our data do not support this, as affected subjects displayed normal cognition. Large variability was observed in the age of onset (a)symmetry, severity and progression rate of HI. About half of the affected individuals displayed vestibular dysfunction and experienced symptoms thereof. The late-onset progressive phenotype and the absence of cochleovestibular malformations on computed tomography scans indicate that heterozygous defects of LMX1A do not result in severe developmental abnormalities in humans. We propose that a single LMX1A wild-type copy is sufficient for normal development but insufficient for maintenance of cochleovestibular function. Alternatively, minor cochleovestibular developmental abnormalities could eventually lead to the progressive phenotype seen in the families
Mycobacterium abscessus, an uncommon cause of chronic otitis media
Otitis media with otorrhea is common in children. Worldwide, 4% of all otitis media in children is caused by tuberculous otitis media.(1) Otitis media due to a nontuberculous mycobacterium (NTM) is uncommon. Since the description of the first case in 1976, only 31 well- documented cases of middle ear infections caused by NTM have been reported.(1-3) Originally, NTM were divided into 4 groups using the Runyon classification, based on growth rate and pigment production.(4) However, in recent years more accurate species-specific identification by means of molecular techniques are available.(5) Due to the increase of immunosuppressive conditions, the incidence of NTM infections has also increased.(2) A relatively common NTM infection is cervical lymphadenitis.(1,2,6,7
Persistent trigeminal artery associated with trigeminal neuralgia: hypothesis of neurovascular compression
Cochlear implantation in a patient with deafness induced by CharcotβMarieβTooth disease (hereditary motor and sensory neuropathies)
The etiology of idiopathic sudden sensorineural hearing loss - Experimental herpes simplex virus infections of the inner ear
The etiology of idiopathic sudden sensorineural hearing loss - Experimental herpes simplex virus infections of the inner ear
Hypothesis: Experimentally induced herpes simplex virus type 1 (HSV-1) labyrinthitis provides a suitable model for idiopathic sudden sensorineural hearing loss (ISSHL). Background: Viral labyrinthitis has been postulated to play a role in the pathophysiology of ISSHL. Circumstantial evidence is painting at members of the herpes virus family. Experimental viral labyrinthitis elicited by various virus families leaves a virus-specific pattern of cochlear damage. Herpes viruses provide the best matching pattern in the distribution of cochlear damage when compared with ISSHL postmortem cochlear histopathology. Methods: Herpetic viral labyrinthitis was induced in guinea pigs using perilymphatic inoculation with HSV-1. A control group was inoculated with the culture medium only. Infection was confirmed by the measurement of HSV antibodies. Hearing was monitored. Cochlear damage was evaluated by light and electron microscopy. Results: In all HSV-1 inoculated animals, rapid loss of hearing occurred. Seroconversion took place, but no systemic manifestations of herpetic infection were observed. The control group showed no cochlear or systemic symptoms. When comparing cochlear histopathology in ISSHL to experimental viral HSV-1 labyrinthitis, strong similarities were found: degeneration of the stria vascularis, destruction of the organ of Corti, loosening of the tectorial membrane, and inflammatory changes in neural structures. Conclusions: Based on clinical and histopathologic characteristics, experimental HSV-1 labyrinthitis provides a suitable model of ISSHL
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