2,763 research outputs found

    Quantum dot states and optical excitations of edge-modulated graphene nanoribbons

    Get PDF
    We investigate from first principles the electronic and optical properties of edge-modulated armchair graphene nanoribbons, including both quasiparticle corrections and excitonic effects. Exploiting the oscillating behavior of the ribbon energy gap, we show that minimal width-modulations are sufficient to obtain confinement of both electrons and holes, thus forming optically active quantum dots with unique properties, such as the coexistence of dotlike and extended excitations and the fine tunability of optical spectra, with great potential for optoelectronic applications

    "Twin lesions". which one is the bad one. improvement of clinical diagnosis with reflectance confocal microscopy

    Get PDF
    BACKGROUND: In vivo reflectance confocal microscopy (RCM) is a novel non-invasive diagnostic tool, which is used to differentiate skin lesions. Even in lesions with similar dermatoscopic images, RCM may improve diagnostic accuracy. METHODS: Three sets of false "twin lesions" with similar macroscopic and dermatoscopic images are matched. All lesions are evaluated with RCM and lesions are excised for further evaluation. Corresponding features in confocal images, dermatoscopy and histopathology are discussed. RESULTS: In all matched pairs, one of the lesions was diagnosed as melanoma with the observation of melanoma findings such as: epidermal disarray, pagetoid cells in epidermis and cellular atypia at the junction. Benign lesions were differentiated easily with RCM imaging. CONCLUSION: Examining dermatoscopically difficult and/or similar lesions with RCM facilitates diagnostic and therapeutic decision making. Using RCM in daily practice may contribute to a decrease in unnecessary excisions

    Exciton binding energies in carbon nanotubes from two-photon photoluminescence

    Full text link
    One- and two-photon luminescence excitation spectroscopy showed a series of distinct excitonic states in single-walled carbon nanotubes. The energy splitting between one- and two-photon-active exciton states of different wavefunction symmetry is the fingerprint of excitonic interactions in carbon nanotubes. We determine exciton binding energies of 0.3-0.4 eV for different nanotubes with diameters between 0.7 and 0.9 nm. Our results, which are supported by ab-initio calculations of the linear and non-linear optical spectra, prove that the elementary optical excitations of carbon nanotubes are strongly Coulomb-correlated, quasi-one dimensionally confined electron-hole pairs, stable even at room temperature. This alters our microscopic understanding of both the electronic structure and the Coulomb interactions in carbon nanotubes, and has direct impact on the optical and transport properties of novel nanotube devices.Comment: 5 pages, 4 figure

    Dynamical-charge neutrality at a crystal surface

    Get PDF
    For both molecules and periodic solids, the ionic dynamical charge tensors which govern the infrared activity are known to obey a dynamical neutrality condition. This condition enforces their sum to vanish (over the whole finite system, or over the crystal cell, respectively). We extend this sum rule to the non trivial case of the surface of a semiinfinite solid and show that, in the case of a polar surface of an insulator, the surface ions cannot have the same dynamical charges as in the bulk. The sum rule is demonstrated through calculations for the Si-terminated SiC(001) surface.Comment: 4 pages, latex file, 1 postscript figure automatically include

    Lighten UP! A community-based group intervention to promote psychological well-being in older adults

    Get PDF
    Objectives: Aging is often characterized by declines in physical and mental health and increased risk for depression and social isolation. A protective factor that has been found to effectively moderate these phenomena is psychological well-being. The aim of his study was to pilot test a novel group intervention (Lighten UP! program) for the promotion of psychological well-being in older adults living in the community. Methods: Lighten UP! is an eight-week program consisting of 90-minute group session designed to teach participants to identify and savor positive experiences across multiple domains of eudaimonic well-being. It was delivered to a sample of 103 men and women aged 60 or over, that were assessed pre- and post-intervention with Ryff's Psychological Well-being Scale (PWB), Life Satisfaction scale, Geriatric Depression Scale, Symptom Questionnaire, and items measuring sleep complaints and social well-being. Results: At the end of the eight weeks, participants reported significantly increased PWB, life satisfaction, and social well-being along with lower levels of depression and fewer physical symptoms and sleep complaints. These gains were particularly robust for individuals with lower pre-program levels of PWB. Conclusions: This pilot investigation suggests the feasibility of a short group program for enhancing well-being in older adults. Future controlled investigations with long-term follow-up assessment are needed to confirm the effectiveness and sustained benefits of the Lighten UP! program. © 2015 Taylor & Franci

    Optical properties and charge-transfer excitations in edge-functionalized all-graphene nanojunctions

    Full text link
    We investigate the optical properties of edge-functionalized graphene nanosystems, focusing on the formation of junctions and charge transfer excitons. We consider a class of graphene structures which combine the main electronic features of graphene with the wide tunability of large polycyclic aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we show that, upon convenient choice of functional groups, low energy excitations with remarkable charge transfer character and large oscillator strength are obtained. These properties can be further modulated through an appropriate width variation, thus spanning a wide range in the low-energy region of the UV-Vis spectra. Our results are relevant in view of designing all-graphene optoelectronic nanodevices, which take advantage of the versatility of molecular functionalization, together with the stability and the electronic properties of graphene nanostructures.Comment: J. Phys. Chem. Lett. (2011), in pres

    Optical coherence tomography for patch test grading: A prospective study on its use for noninvasive diagnosis of allergic contact dermatitis

    Get PDF
    Background: The diagnosis of allergic contact dermatitis should be confirmed by skin patch tests. Distinguishing between irritant and allergic reactions is sometimes difficult. Objectives: To analyse the in vivo morphological changes in patch test reactions compared to healthy skin, and to detect subclinical changes in doubtful reactions using optical coherence tomography (OCT). To develop an OCT-based algorithm to support patch-test grading. Methods: One hundred twenty-nine skin patch-test areas were scanned with OCT to evaluate the following features: architectural and vascular morphology, epidermal thickness, optical attenuation coefficient (AC), and blood flow at 0.1, 0.2, and 0.35 mm depth. Results: Most common OCT features of acute contact allergic reactions in patch tests were spongiosis with microvesicles (94.8%), macrovesicles (60.3%), and coalescing vesicles (46.6%), the latter useful in differentiating acute allergic from irritant dermatitis (P-value <.05). Objective quantitative parameters correlated well with the severity grade: epidermal thickness due to spongiosis, AC (P-value <.05) and blood flow at 0.2 and 0.35 mm (P-value <.01). Conclusions: OCT as a noninvasive diagnostic tool, established for skin cancer diagnosis, is useful for evaluating contact allergic patch-test reactions. Not only morphological but also objective features such as blood flow and AC correlate with the reaction severity. Further studies are needed to explore the differences in irritant and allergic contact dermatitis

    Line-Field Confocal Optical Coherence Tomography Increases the Diagnostic Accuracy and Confidence for Basal Cell Carcinoma in Equivocal Lesions: A Prospective Study

    Get PDF
    Diagnosing clinically unclear basal cell carcinomas (BCCs) can be challenging. Line-field confocal optical coherence tomography (LC-OCT) is able to display morphological features of BCC subtypes with good histological correlation. The aim of this study was to investigate the accuracy of LC-OCT in diagnosing clinically unsure cases of BCC compared to dermoscopy alone and in distinguishing between superficial BCCs and other BCC subtypes. Moreover, we addressed pitfalls in false positive cases. We prospectively enrolled 182 lesions of 154 patients, referred to our department to confirm or to rule out the diagnosis of BCC. Dermoscopy and LC-OCT images were evaluated by two experts independently. Image quality, LC-OCT patterns and criteria, diagnosis, BCC subtype, and diagnostic confidence were assessed. Sensitivity and specificity of additional LC-OCT were compared to dermoscopy alone for identifying BCC in clinically unclear lesions. In addition, key LC-OCT features to distinguish between BCCs and non-BCCs and to differentiate superficial BCCs from other BCC subtypes were determined by linear regressions. Diagnostic confidence was rated as \u201chigh\u201d in only 48% of the lesions with dermoscopy alone compared to 70% with LC-OCT. LC-OCT showed a high sensitivity (98%) and specificity (80%) compared to histology, and these were even higher (100% sensitivity and 97% specificity) in the subgroup of lesions with high diagnostic confidence. Interobserver agreement was nearly perfect (95%). The combination of dermoscopy and LC-OCT reached a sensitivity of 100% and specificity of 81.2% in all cases and increased to sensitivity of 100% and specificity of 94.9% in cases with a high diagnostic confidence. The performance of LC-OCT was influenced by the image quality but not by the anatomical location of the lesion. The most specific morphological LC-OCT criteria in BCCs compared to non-BCCs were: less defined dermoepidermal junction (DEJ), hyporeflective tumor lobules, and dark rim. The most relevant features of the subgroup of superficial BCCs (sBCCs) were: string of pearls pattern and absence of epidermal thinning. Our diagnostic confidence, sensitivity, and specificity in detecting BCCs in the context of clinically equivocal lesions significantly improved using LC-OCT in comparison to dermoscopy only. Operator training for image acquisition is fundamental to achieve the best results. Not only the differential diagnosis of BCC, but also BCC subtyping can be performed at bedside with LC-OCT

    Line-field optical coherence tomography: in\ua0vivo diagnosis of basal cell carcinoma subtypes compared with histopathology

    Get PDF
    Background: Basal cell carcinoma (BCC) is the most common skin cancer in the general population. Treatments vary from Mohs surgery to topical therapy, depending on the subtype. Dermoscopy, reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) have gained a foothold in daily clinical practice to optimize diagnosis and subtype-oriented treatment. The new technique of line-field confocal OCT (LC-OCT) allows imaging at high resolution and depth, but its use has not yet been investigated in larger studies. Aim: To evaluate the main LC-OCT criteria for the diagnosis and subtyping of BCC compared with histopathology, OCT and RCM. Methods: In total, 52 histopathologically confirmed BCCs were evaluated for imaging criteria. Their frequency, predictive values and ROC curves were calculated. A multinominal regression with stepwise variables selection to distinguish BCC subtypes was performed. Results: Nodular BCCs were mainly characterized by atypical keratinocytes, altered dermoepidermal junction (DEJ), tumour nests in the dermis, dark clefting, prominent vascularization and white hyper-reflective stroma. Superficial BCCs showed a thickening of the epidermis due to a series of tumour lobules with clear connection to the DEJ (string of pearls pattern). Infiltrative BCCs were characterized by elongated hyporeflective tumour strands, surrounded by bright collagen (shoal of fish pattern). The overall BCC subtype agreement between LC-OCT and conventional histology was 90.4% (95% CI 79.0\u201396.8). Conclusion: LC-OCT allows noninvasive, real-time identification of BCCs and their subtypes in vertical, horizontal and three-dimension mode compared with histology, RCM and OCT. Further larger studies are needed to better explore the clinical applications of this promising device
    • …
    corecore