Adaptive tuning of infrared emission using VO2 thin films.

Phase-transition materials provide exciting opportunities for controlling optical properties of photonic devices dynamically. Here, we systematically investigate the infrared emission from a thin film of vanadium dioxide (VO2). We experimentally demonstrate that such thin films are promising candidates to tune and control the thermal radiation of an underlying hot body with different emissivity features. In particular, we studied two different heat sources with completely different emissivity features, i.e. a black body-like and a mirror-like heated body. The infrared emission characteristics were investigated in the 3.5-5.1 µm spectral range using the infrared thermography technique which included heating the sample, and then cooling back. Experimental results were theoretically analyzed by modelling the VO2 film as a metamaterial for a temperature range close to its critical temperature. Our systematic study reveals that VO2 thin films with just one layer 80 nm thick has the potential to develop completely different dynamic tuning of infrared radiation, enabling both black-body emission suppression and as well as mirror emissivity boosting, in the same single layer device. Understanding the dynamics and effects of thermal tuning on infrared emission will benefit wide range of infrared technologies including thermal emitters, sensors, active IR filters and detectors.

Polarization insensitive infrared absorbing behaviour of one-dimensional multilayer stack: a fractal approach.

The control and tailoring of infrared absorbance/emittance is a crucial task for all those applications involving thermal radiation management and detection. We theoretically investigated the peculiar absorbing/emitting behaviour of pre-fractal Cantor multilayers, in order to design a polarization-insensitive multilayer stack absorbing over a wide angular lobe in the mid wavelength infrared range (8-10 µm). Using transfer matrix method, we explored the spectral properties arising from both the material and the geometrical dispersion. We considered several combinations of the constituent materials: SiO2 was combined with TiO2 and Si, respectively.

Pre-fractal multilayer structure for polarization- insensitive temporally and spatially coherent thermal emitter.

We investigate electromagnetic wave propagation through one-dimensional stacks arranged as truncated pre-fractal Cantor multilayer. Taking into account materials' dispersion as well as real absorptive losses, we studied the spectral and spatial emissivity in both on-axis and off-axis direction. The typical cavity mode resonances associated to the pre-fractal structure are exploited to design a polarization-insensitive infrared emitter pertaining both temporal and spatial coherence.

Evidence of multipolar response of Bacteriorhodopsin by noncollinear second harmonic generation.

Noncollinear second harmonic generation from a Bacteriorhodopsin (BR) oriented multilayer film was systematically investigated by varying the polarization state of both fundamental beams. Both experimental results and theoretical simulations, show that the resulting polarization mapping is an useful tool to put in evidence the optical chirality of the investigated film as well as the corresponding multipolar contributions to the nonlinear.

The gymnast's shoulder MRI and clinical findings.

AIM: The aim of the study was to evaluate effects of shoulder overuse in elite symptomatic or asymptomatic gymnasts. METHODS: This was a university-based sport traumatology research, a cohort study, with a control group comparison. Patients included were: 21 elite male gymnasts performing in the Italian National team for at least 10 years and a control group of 10 patients (20 shoulders) of the same age and sex, randomly selected among a healthy non-athletic population who underwent shoulder MRI. Magnetic resonance imaging without contrast were performed to all participants and clinical findings were summarized. Two experienced musculoskeletal radiologists interpreted each MRI scan for multiple variables (rotator cuff tendons, labral signal, capsule), including type of measurements performed on soft tissues (muscles, tendons) to assess global modifications of the shoulders. RESULTS: Signal abnormalities were detected in 36/36 (100%) gymnasts' shoulders, and in 4/20 (20%) of the controls. Sixteen of 36 (44.4%) shoulders had findings consistent with SLAP tears, bilateral in four patients; anteroinferior labrum lesions were identified in 10/36 (27.7%) shoulders, as compared with none (0%) in the controls. Eight of 36 (22%) shoulders had findings consistent with partial- or full-thickness tears of the rotator cuff as compared with none (0%) of the controls. Increased thickness of rotator cuff tendons and hypertrophy of rotator cuff muscles and deltoid muscles were recorded: such reports were symmetrical between dominant and non dominant arms, and increased when compared to controls. CONCLUSION: Gymnasts' shoulders are significantly different from those of the general population. MRI findings, especially SLAP tears, and hypertrophy are symmetrical. SLAP tears seem to be responsible of most early retirement.

Circular dichroism in the optical second-harmonic emission of curved gold metal nanowires.

Here we report the experimental observation of circular dichroism in the second-harmonic field (800-400 nm conversion) generated by self-organized gold nanowire arrays with subwavelength periodicity (160 nm). Such circular dichroism, raised by a nonlinear optical extrinsic chirality, is the evident signature of the sample morphology. It arises from the curvature of the self-assembled wires, producing a lack of symmetry at oblique incidence. The results were compared, both in the optical linear and nonlinear regime, with a reference sample composed of straight wires. Despite the weak extrinsic optical chirality of our samples (not observable by our optical linear measurements), high visibility (more than 50%) was obtained in the second-harmonic generated field.

Optical polarization based logic functions (XOR or XNOR) with nonlinear Gallium nitride nanoslab.

We present a scheme of XOR/XNOR logic gate, based on non phase-matched noncollinear second harmonic generation from a medium of suitable crystalline symmetry, Gallium nitride. The polarization of the noncollinear generated beam is a function of the polarization of both pump beams, thus we experimentally investigated all possible polarization combinations, evidencing that only some of them are allowed and that the nonlinear interaction of optical signals behaves as a polarization based XOR. The experimental results show the peculiarity of the nonlinear optical response associated with noncollinear excitation, and are explained using the expression for the effective second order optical nonlinearity in noncollinear scheme.

Mapping the nonlinear optical susceptibility by noncollinear second-harmonic generation.

We present a method, based on noncollinear second-harmonic generation, to evaluate the nonzero elements of the nonlinear optical susceptibility. At a fixed incidence angle, the generated signal is investigated by varying the polarization state of both fundamental beams. The resulting polarization charts allows us to verify if Kleinman's symmetry rules can be applied to a given material or to retrieve the absolute value of the nonlinear optical tensor terms, from a reference measurement. Experimental measurements obtained from gallium nitride layers are reported. The proposed method does not require an angular scan and thus is useful when the generated signal is strongly affected by sample rotation.

Bound and free waves in non-collinear second harmonic generation.

We analyze the relationship between the bound and the free waves in the noncollinear SHG scheme, along with the vectorial conservation law for the different components arising when there are two pump beams impinging on the sample with two different incidence angles. The generated power is systematically investigated, by varying the polarization state of both fundamental beams, while absorption is included via the Herman and Hayden correction terms. The theoretical simulations, obtained for samples which are some coherence length thick show that the resulting polarization mapping is an useful tool to put in evidence the interference between bound and free waves, as well as the effect of absorption on the interference pattern.

Fibro-cartilaginous lesions of the glenoid labrum in shoulder instability: a proposed classification using sagittal-oblique arthro-MRI.

PURPOSE: To propose a graded classification of lesions of the fibrocartilaginous glenoid labrum in traumatic dislocations of the shoulder, based on arthro-MRI in sagittal-oblique views. MATERIALS AND METHODS: Seventy-one patients with histories of chronic post-traumatic shoulder instability were studied from May 2000 to May 2001. MR images were obtained using superconducting magnets operating at 1 and 1.5 Tesla, with a dedicated shoulder coil. The study was carried out in combination with arthrography, with axial sections oriented perpendicularly to the longitudinal axis of the glena, oblique coronal sections parallel to the course of the supraspinous muscle tendon and oblique sagittal sections with axis parallel to the longitudinal axis of the glena. RESULTS: In one case an anatomical variant was found (Buford complex). In 18 patients a simple fissuration of the fibrocartilaginous glenoid labrum was found, whereas 28 patients displayed more extensive lesions affecting the middle-inferior portions of the labrum. In 15 patients the lesion extended to the middle-superior third of the glena, involving the middle glenohumeral ligament. In 9 cases, in addition to a complete lesion of the labrum, with typical "bucket-handle" appearance, a lesion of the superior and middle glenohumeral ligaments was also observed. DISCUSSION AND CONCLUSIONS: In traumatic shoulder dislocations it is essential to provide the surgeon with precise information regarding the location, extension and degree of damage to the capsule, ligaments and especially the labrum of the glenohumeral joint. On the basis of the results obtained in the sagittal-oblique sections we propose an MR-arthrography classification dividing lesions of the fibrocartilaginous labrum into 4 grades.

[Ankle impingement syndrome]. / Sindrome conflittuale della caviglia.

PURPOSE: The ankle impingement syndrome depends on many factors (fiber or bone production changes) manifested with pain and limited range of movement of the tibiotarsal joint. We tried to classify the various causes and sites of impingement syndromes with MRI. MATERIALS AND METHODS: A cohort of 42 selected patients underwent a 2-year orthopedic follow-up. All patients were examined with MRI using both a low field permanent dedicated magnet at 0.2 Tesla (Artoscan, Esaote Biomedica, Genoa, Italy) and a high field General Electric unit at 1.0 T; sequences and views were chosen according to the condition studied. Gd-DTPA was administered in 26/42 patients. All patients underwent arthroscopy. RESULTS: Twenty-one patients had positive symptoms in the anterolateral region of the ankle and 14 of them had lateral changes. In 13 patients we found fibrous tissue (meniscoid lesion) or hypertrophy of the synovial tissue. An intra-articular body was observed in one patient. An osteophyte was found in 5 patients at the level of the anterior margin of the tibia, with the presence of reactive synovial tissue. Three of 18 patients with posterior pain had a traumatic injury of the posterior exterior tubercle of the astragalus, 7 had a fracture of the os trigonum and 2 had small sclerotic foci formations in calceneal site; chondropathy with sclerosis of subchondral bone was diagnosed in 2 patients. Posterior bone impingement was observed in the remaining 4 patients. Two patients had synovial impingement in posterolateral site. A posterior plica synovialis was seen in 1 patient. Fibrotic-scar tissue was observed in one case, in the subtalus region (impingement synovialis subtalaris). The administration of intra-articular Gd-DTPA provided better definition of the fibrous tissue and the intra-articular free bodies. Modest vascular enhancement of the tissues was seen in 9 of 8 patients receiving the contrast agent. In the other two cases, where signal tissue was low, no signal enhancement was observed after the contrast agent administration. DISCUSSION: Based on integrated MR, clinical and arthroscopic findings we classified tibiotarsal joint impingement syndromes into three types, namely: 1) bone impingement; 2) fibrous impingement where both site and grade are considered; 3) impingement synovialis subtalaris. CONCLUSIONS: MRI appears to be a fundamental diagnostic imaging tool in depicting and detailing the various patterns and sites of the impingement syndrome of the tibiotarsal joint thus allowing an objective classification.

[New prospects in the assessment of the knee extensor complex with dynamic magnetic resonance]. / Nuove prospettive nella valutazione con Risonanza Magnetica dinamica del complesso estensore del ginocchio.

INTRODUCTION: Altered patellofemoral biomechanics may result in pain, instability and early involutive processes. Magnetic Resonance Imaging (MRI), with its panoramic capabilities, has proved to be an effective technique in the study of knee extensor complex changes. The diagnostic advantages of dynamic studies of patellofemoral kinetics are reported in the recent scientific literature. We investigated the diagnostic potentials of passive studies of the knee extensor complex with sagittal and axial cine MRI. Then, we developed and optimized an innovative study method overcoming the limitations of the other dynamic techniques for the correct assessment of patellofemoral biomechanics. MATERIAL AND METHODS: We studied the knee with a .2 T permanent magnet dedicated to the limbs and acquired the images in different positions of flexion-extension with T1-weighted SE and T2-weighted GE sequences. We examined 21 healthy volunteers and 37 of 38 patients with anterior knee joint pain of suspected patellofemoral origin. All the images needed for dynamic studies were acquired in about 20 minutes. For the scan planes not to be affected by patellar motion in the different degrees of knee extension, it is necessary to acquire single axial images to be edited in cine motion afterwards. Each acquisition is aligned along sagittal reference planes depiciting always the same patellar aspect. RESULTS: Significant correlations were found between clinical and cine MR findings in 25 patients. In particular we depicted some extensor complex impingement conditions missed at conventional MRI, which clarified the role played by patellar dysplastic changes in cartilage microtraumas. Our technique was accurate, quite easy to perform and repeatable. We performed cost-effective dynamic studies which were useful in the evaluation of patients with anterior knee pain in whom conventional MRI had failed to provide enough information. CONCLUSIONS: Our technique differs from other passive or active dynamic studies reported on in the literature because the patellar volume does not change during acquisitions. This permits to decrease morphological changes and to simplify, on cine MR reconstructions, the specific analysis of patellofemoral dynamics during flexion-extension. Fewer morphological changes also mean a more accurate analysis showing the role of patellar dysplasia in cartilage microtraumas. Our dynamic MR protocol is accurate, easy to perform and to repeat; it allows dynamic studies in the patients with poor static MR findings.

Knee impingement syndromes.

INTRODUCTION: The so-called knee impingement syndromes are very frequently reported in both professional and amateur sportsmen. PURPOSE: The objective of our study was to classify the most frequent knee changes responsible for such syndromes considering both pathology and diagnostic work-up. MATERIAL AND METHODS: Our patients complained of aspecific symptoms related to articular meniscal, ligament or cartilage, conditions. The site of pain was periarticular and there was no apparent sign of acute traumatic events. All individuals, aged 16-55, practised sports at different levels and women were the majority of the sample. The study was carried out from 1995 to 1997 and all the medical records presented in occasion of the sports-medicine check-up were reviewed. RESULTS: The sites of symptom onset were divided into medial, lateral, anterior and posterior. For each of them the most frequent conditions which could be defined as impingement syndromes, were defined paying particular attention to the possible methods of diagnosis useful to classify the disorder. As for anterior syndromes, patellofemoral disorders were the most frequent findings. They were associated with either incorrect torsion movements of the lower limbs or local dysplasia. Alterations in the single skeletal and cartilage structures were reported. Always referring to anterior syndromes, Hoffa's fat pad imflammation and the jumper's knee were a less frequent finding. As for posterior impingement syndromes, the most frequent abnormalities involved the insertional tract of the midcalf muscle associated with bursa reaction and insertional popliteus hypertrophy. As for medial syndromes, the most frequent abnormality involved the parapatellar synovial fold whose symptoms can be often mistaken for a meniscal injury. Less frequent is the involvement of the 'pes anserinus' tendinitis and the insertional enthesopathy of the semimembranosus muscle. As for lateral syndromes, the phlogistic involvement of the distal insertional tract of the broad fascia tensor tendon with bursa reaction is very frequently reported, while the inflammation of the popliteal tendon and of the femoral bicipital tendon is less common. CONCLUSIONS: Although less frequent than meniscal and ligament injuries, impingement syndromes must be taken into due consideration when looking for knee disorders resorting to different diagnosis methods. Diagnostic imaging is very useful in this regard as it allows a proper and correct diagnosis procedure for any single condition.

[Role of magnetic resonance in the evaluation of the normal and osteochondrosis hip in early and late childhood]. / Ruolo della Risonanza Magnetica nella valutazione dell'anca normale e osteocondrosica nella prima e seconda infanzia.

INTRODUCTION: Despite MR potentials, few studies investigate the features of normal hips and of hip osteochondrosis in early and late childhood. We report our personal experience with MRI of hip osteochondrosis in pediatric patients. MATERIAL AND METHODS: MR images were obtained with total body MR equipment at medium and high fields. The normal hips were studied in children aged 34 months to 6 years with abdominal-urinary tract disorders and in 9 patients of the same age with unilateral Perthes disease. Hip osteochondrosis was studied in 6 children with Catteral's type III and IV and in 3 with type I and II disease. General anesthesia was never necessary to perform MRI. RESULTS: MRI exactly defined the cephalic anatomic profiles of normal hips which are not depicted with conventional radiography before the femoral head cartilage ossifies completely. MR contrast resolution was very high in depicting the maturation of the epiphyseal nucleus and its exact site in the cartilagineous epiphyseal hemisphere proximal to the femur. The analysis of MR morphological and structural changes permitted to correlate MR findings with the histopathologic features described in the literature. In addition, MRI of childhood hip osteochondrosis showed maked structural changes of the epiphyseal nucleus which are usually missed with conventional radiography. MRI permits early location of the abnormal area and the recognition of growing disk abnormalities; it also shows the whole cephalic cartilage and the changes of the epiphyseal nucleus evolution, which permits to differentiate osteochondrosis evolution from recessive patterns. Finally, MRI clearly showed the increased equatorial diameters of the involved femoral heads and the associated decrease in polar diameters, which is essential to study the biomechanics of hip osteochondrosis and therefore to plan treatment. CONCLUSIONS: MRI, even with coronal sequences and T1-weighting only, permits: 1) to image normal hips and hip osteochondrosis, especially in early and late childhood; 2) to clearly define cephalocotyloid relationships; 3) to depict the actual anatomic margins of the head and its structure; 4) to investigate the head cartilage extent and to locate the ossification nucleus. These morphologic and structural data are very useful to diagnose and manage hip osteochondrosis in the evolutive age. MRI shows abnormal changes in anatomic structures which are not seen with conventional radiography and demonstrates the evolution of the osteochondrosis process over time. In children over six, at the end of the ossification process of the head cartilage, conventional radiography alone is often sufficient to depict cephalocotyloid relationships and the MR diagnostic criteria of bone-cephalic diseases are similar to those used in adult hip studies.

Sonographic findings in haemodialysis-related chronic arthropathy.

In 33 subjects receiving long-term haemodialysis sonographic examination of shoulders, hips and knees was performed. Changes of both joints and periarticular soft tissues were found in 60 shoulders, 16 hips and 42 knees. In the shoulder besides the presence of tenosynovitis and bursitis, even significant thickening of rotator cuff and increased distance between capsule and bone in transascellar scan were found. Also, in the hip the distance between capsule and bone was significantly increased. In the knee effusion was present in 14 cases and synovial hypertrophy in 20. Articular femoral cartilage was significantly thinned. Results obtained suggest the hypothesis of the presence of an important inflammatory component in the pathogenesis of arthropathy related to haemodialytic treatment. The production of cytokines by mononuclear cells stimulated by beta-2 microglobulin may cause the inflammatory response. Sonographic findings of alterations in 42 symptomless joints show the importance of this diagnostic method to begin an early therapy.