Optical properties of individual CdS/CdSe/CdS nanocrystals: spherical quantum wells as single-photon sources.

We have synthesized CdS(1.3 nm)/CdSe(1.7 nm)/CdS(3.4 nm) spherical quantum wells (SQWs) with a diameter of 13 nm and demonstrated the first photon-antibunching from their emission, labelling them as single-photon sources. Antibunching survives even at high excitation intensities, ruling-out strong emission from the bi-exciton. For the largest intensities, antibunching coupled to spectral measurements reveal the signature of a blue-shifted emission, associated to an irreversible photo-aging effect. A statistical analysis over 26 SQWs demonstrates a moderate correlation between the energy of the main and the blue-shifted emission. Intensity-timetraces recorded on 28 single SQWs show weak blinking, with a median time spent in the bright state of 89%. Their emission decay reveals a complex dynamic with either three or four exponential components. We assigned three of them to the neutral and singly-charged excitons and the slowest to defect emission. While SQWs have been initially designed for laser-oriented applications, we demonstrate that they can serve as efficient single-photon sources.

Internal quantum efficiency of AlGaN/AlN quantum dot superlattices for electron-pumped ultraviolet sources.

In this paper, we describe the growth and characterization of ≈530 nm thick superlattices (100 periods) of AlxGa1-xN/AlN (0 ⩽ x ⩽ 0.1) Stranski-Krastanov quantum dots (QDs) for application as the active region of electron-beam pumped ultraviolet lamps. Highly dense (>1011 cm-2) QD layers are deposited by molecular beam epitaxy, and we explore the effect of the III/V ratio during the growth process on their optical performance. The study considers structures emitting in the 244-335 nm range at room temperature, with a relative linewidth in the 6%-11% range, mainly due to the QD diameter dispersion inherent in self-assembled growth. Under electron pumping, the emission efficiency remains constant for acceleration voltages below ≈9 kV. The correlation of this threshold with the total thickness of the SL and the penetration depth of the electron beam confirms the homogeneity of the nanostructures along the growth axis. Below the threshold, the emission intensity scales linearly with the injected current. The internal quantum efficiency (IQE) is characterized at low injection, which reveals the material properties in terms of non-radiative processes, and high injection, which emulates carrier injection in operation conditions. In QDs synthesized with III/V ratio <0.75, the IQE remains around 50% from low injection to pumping power densities as high as 200 kW cm-2, being the first kind of nanostructure that present such stable behaviour.

Radio-luminescence spectral features and fast emission in hafnium dioxide nanocrystals.

In this work, we investigate the optical properties of hafnium dioxide nanocrystals, upon X-ray irradiation, looking for spectral evolution following thermal treatments in air up to 1000 °C that modify the crystal size as well as their point defect concentrations. Radio-luminescence measurements from 10 K up to room temperature reveal a rich and evolving picture of the optical features. A complete spectral analysis of the broad luminescence spectra reveals the presence of several emission components in the visible and UV regions. The lower energy components peaking at 2.1, 2.5, and 2.9 eV are characterized by a thermal quenching energy of 0.08 eV, while the corresponding value for the UV bands at 4.1 and 4.7 eV is close to 0.23 eV. We tentatively assign the components ranging from 2 to 3 eV to the presence of optically active defects of an intrinsic nature, together with the occurrence of titanium impurities; conversely, the bands at higher energies are likely to be of an excitonic nature. The comparison with previous photo-luminescence studies allows evidencing characteristic differences between the features of luminescence emissions caused by intra-centre excitation and those occurring under ionizing irradiation. Finally, scintillation measurements in the visible range reveal the existence of a fast decay in the nanosecond time scale for the smallest hafnia nanocrystals. This study offers a clear description of HfO2 luminescence characteristics upon excitation by X-rays and can lead to a better comprehension of the structure-property relationship at the nanoscale in metal oxides.

Stimulated scintillation emission depletion X-ray imaging.

X-ray microtomography is a widely applied tool for noninvasive structure investigations. The related detectors are usually based on a scintillator screen for the fast in situ conversion of an X-ray image into an optical image. Spatial resolution of the latter is fundamentally diffraction limited. In this work, we introduce stimulated scintillation emission depletion (SSED) X-ray imaging where, similar to stimulated emission depletion (STED) microscopy, a depletion beam is applied to the scintillator screen to overcome the diffraction limit. The requirements for the X-ray source, the X-ray flux, the scintillator screen, and the STED beam were evaluated. Fundamental spatial resolution limits due to the spread of absorbed X-ray energy were estimated with Monte Carlo simulations. The SSED proof-of-concept experiments demonstrated 1) depletion of X-ray excited scintillation, 2) partial confinement of scintillating regions to sub-diffraction sized volumes, and 3) improvement of the imaging contrast by applying SSED.

Shells of crystal field symmetries evidenced in oxide nano-crystals.

By the use of a point charge model based on the Judd-Ofelt transition theory, the luminescence from Eu(3+) ions embedded in Gd(2)O(3) clusters is calculated and compared to the experimental data. The main result of the numerical study is that without invoking any other mechanisms such as crystal disorder, the pure geometrical argument of the symmetry breaking induced by the particle surface has an influence on the energy level splitting. The modifications are also predicted to be observable in realistic conditions where unavoidable size dispersion has to be taken into account. The emission spectrum results from the contribution of three distinct regions; a cluster core, a cluster shell and the very surface, the latter being almost completely quenched in realistic conditions. Eventually, by detailing the spectra of the ions embedded at different positions in the cluster we get an estimate of about 0.5 nm for the extent of the crystal field induced Stark effect. Due to the similarity between Y (2)O(3) and Gd(2)O(3), these results also apply to Eu(3+) doped Y(2)O(3) nanoparticles.

Highly luminescent scintillating hetero-ligand MOF nanocrystals with engineered Stokes shift for photonic applications.

Large Stokes shift fast emitters show a negligible reabsorption of their luminescence, a feature highly desirable for several applications such as fluorescence imaging, solar-light managing, and fabricating sensitive scintillating detectors for medical imaging and high-rate high-energy physics experiments. Here we obtain high efficiency luminescence with significant Stokes shift by exploiting fluorescent conjugated acene building blocks arranged in nanocrystals. Two ligands of equal molecular length and connectivity, yet complementary electronic properties, are co-assembled by zirconium oxy-hydroxy clusters, generating crystalline hetero-ligand metal-organic framework (MOF) nanocrystals. The diffusion of singlet excitons within the MOF and the matching of ligands absorption and emission properties enables an ultrafast activation of the low energy emission in the 100 ps time scale. The hybrid nanocrystals show a fluorescence quantum efficiency of ~60% and a Stokes shift as large as 750 meV (~6000 cm-1), which suppresses the emission reabsorption also in bulk devices. The fabricated prototypal nanocomposite fast scintillator shows benchmark performances which compete with those of some inorganic and organic commercial systems.

Multiple small-intestine intussusceptions: a complication of purpura haemorrhagica in a horse.

A Belgian draft horse stallion presented with classical signs of purpura haemorrhagica: oedema of the distal limbs, ventral abdomen and head, ecchymotic haemorrhage of mucous membranes, epistaxis, fever, lethargy, reluctance to move, and anorexia. Serum chemistry revealed a highly elevated gamma-globulin fraction. Streptococcal lymphadenitis (strangles) had been present on a neighbouring farm in the past few months. After an initial positive response to therapy with benzylpenicillin, flunixin and dexamethasone, the horse's condition deteriorated suddenly on day 4 of hospitalization, with signs of severe endotoxaemia and small-intestine obstruction. The horse was euthanized because of its poor prognosis and because of economic considerations. On necropsy, large serosal haemorrhages in the small and large intestine and multiple jejunojejunal intussusceptions were found. Intussusception is a well-known complication in children with Henoch-Schonlein purpura, a human autoimmune disease resembling purpura haemorrhagica in horses. To the author's knowledge, this is the first report to describe intussusception as a complication of purpura haemorrhagica in a horse.

Pain recognition and treatment in the horse: a survey of equine veterinarians in The Netherlands and Belgium.

This survey investigated the attitudes of equine veterinarians in The Netherlands and the Flemish region of Belgium towards pain management in the horse. Questionnaires were sent out to 771 equine veterinarians, all members of the Dutch or Flemish equine practitioners society. The return rate of completed questionnaires was 16.6%. The survey provided information about the use of analgesic drugs, factors influencing their prescription, pain scoring, analgesic therapy for specific clinical conditions, use of epidural analgesia, and appraisal of personal knowledge of pain management. The pain scores attributed to specific clinical conditions showed considerable variation. Non-steroidal anti-inflammatory drugs (NSAIDS) were the most-often prescribed analgesic drugs, with older drugs still having an important role in pain management. Butorphanol was the main opioid used. A substantial proportion of the respondents considered their knowledge of pain recognition and analgesic therapy to be insufficient or moderate.

Facile and rapid synthesis of highly luminescent nanoparticles via pulsed laser ablation in liquid.

This paper demonstrates the usefulness of pulsed laser ablation in liquids as a fast screening synthesis method able to prepare even complex compositions at the nanoscale. Nanoparticles of Y2O3:Eu3+, Lu2O2S:Eu3+, Gd2SiO5:Ce3+, Lu3TaO7:Gd3+ and Tb3+ are successfully synthesized by pulsed laser ablation in liquids. The phase and stoichiometries of the original materials are preserved while the sizes are reduced down to 5-10 nm. The optical properties of the materials are also preserved but show some small variations and some additional structures which are attributed to the specificities of the nanoscale (internal pressure, inhomogeneous broadening, surface states, etc).

Fluorescent oxide nanoparticles adapted to active tips for near-field optics.

We present a new kind of fluorescent oxide nanoparticle (NP) with properties well suited to active-tip based near-field optics. These particles with an average diameter in the 5-10 nm range are produced by low energy cluster beam deposition (LECBD) from a YAG:Ce3+ target. They are studied by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), cathodoluminescence, near-field scanning optical microscopy (NSOM) and fluorescence in the photon-counting mode. Particles of extreme photo-stability as small as 10 nm in size are observed. These emitters are validated as building blocks of active NSOM tips by coating a standard optical tip with a 10 nm thick layer of YAG:Ce3+ particles directly in the LECBD reactor and by subsequently performing NSOM imaging of test surfaces.

HfO2:X (X = Eu(3+), Ce(3+), Y(3+)) sol gel powders for ultradense scintillating materials.

Hafnium dioxide (HfO 2) presents a high crystalline density which makes it attractive for host lattice activated by rare earths for applications as scintillating materials. HfO 2 powders doped with Eu (3+) or Ce (3+) luminescent ions are prepared by sol gel process. The annealing temperature and the concentration of doping ions are optimized to provide the powder presenting the best scintillation yield. The powders are crystallized in monoclinic phase whatever annealing temperature above 800 degrees C. The emission spectra are characterized by a white broadband between 400 and 600 nm. After optimization, the most efficient composition, namely HfO 2:2.5% Eu 1% Y (molar percent) exhibits a scintillation yield about 31,000 photons/MeV, which is about 3.8 times that of the standard Bi 3Ge 5O 12 (BGO) commercial powder.

CO adsorption on CoMo and NiMo sulfide catalysts: a combined IR and DFT study.

Experimental IR spectra of carbon monoxide adsorbed on a series of Mo/Al2O3, CoMo/Al2O3, and NiMo/Al2O3 sulfided catalysts have been compared to ab initio DFT calculations of CO adsorption on CoMo and NiMo model surfaces. This approach allows the main IR features of CO adsorbed on the sulfide phase to be assigned with an uncertainty of 15 cm(-1). On the CoMo system, the band at 2070 cm(-1) is specific of the promotion by Co and is assigned to CO interacting either with a Co atom or with a Mo atom adjacent to a Co atom. On the NiMo system, CO adsorption on Ni centers of the promoted phase leads to a high-wavenumber band at approximately 2120 cm(-1) that strongly overlaps the band at 2110 cm(-1) characteristic of nonpromoted Mo sites. For NiMo and CoMo catalysts, broad shoulders at low wave numbers (below 2060 cm(-1)) are characteristic of Mo centers adjacent to promoter atoms, indicating a partial decoration of the MoS2 edges by the promoter.

[Rupture of the flexor tendons on an anterior plate for distal radial fracture: four cases and a review of the literature]. / Rupture de tendons fléchisseurs sur plaque antérieure après fracture du radius distal: a propos de 4 cas et revue de la littérature.

We report four cases of flexor tendon ruptures which occurred after distal radial fracture and reviewed the 25 other cases reported in the literature since 1932. Analysis of these 29 cases disclosed the causes of these ruptures. A deformed callus after distal radial fracture or presence of an anterior osteosynthesis plate can under certain conditions lead to secondary flexor tendon tears. It was also found that tears of the flexor pollicis longus rupture predominate, followed by injury to the flexor digitorum profundis and superficialis of the index finger. Other tendons have only been involved in only a few cases. In order to avoid this complication, we propose systematic removal of anterior plates or secondary replacement if the reduction is not totally anatomic. Surgeons should recall the importance of anatomic reduction of distal radial fractures.

Synthesis and properties of europium-based phosphors on the nanometer scale: Eu2O3, Gd2O3:Eu, and Y2O3:Eu.

Nanocrystals of oxides containing europium as the main constituent or as a doping element in RE2O3 ( RE=Y, Gd) have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by high-resolution TEM, absorption spectroscopy, and luminescence spectroscopy. The samples obtained consisted of concentrated and colloidally stable suspensions of luminescent oxide nanoparticles with an average grain diameter in the range 2-5 nm. The nanoparticles were found to be highly crystalline despite their ultrasmall size and the low temperature of 180 degrees C applied during the synthesis. Upon UV excitation, the red luminescence relative to the 5D0-->7Fn transition within the cubic form of RE2O3 exhibits some important differences from that usually found in bulk materials.

[Homolateral transposition of the internal jugular vein for axillo-subclavian venous thrombosis (of effort)]. / Transposition veine jugulaire interne homolatérale pour thrombose veineuse axillo-sous-clavière (d'effort).

UNLABELLED: Indications for treating subclavian vein obstruction are still being developed, especially for endovascular procedures with or without first rib resection. This article explores our experience with chronic and acute subclavian vein thrombosis persisting after medical treatment. In our department of vascular surgery, we have observed 2 cases of subclavian vein obstruction in 2 patients with Paget-Schroetler syndrome who developed major pain and edema in the dominant upper limb. Initially, we managed these patients medically with thrombolysis and anticoagulation. Then, as the significant symptoms persisted and venous thrombolysis developed, we decided on surgical treatment. Because of hypertrophic venous impairment, we used an aggressive procedure with venous bypass using jugular vein transposition and temporary arteriovenous fistula. We observed significant symptom relief and also perfect permeability of the venous bypass at 30 months. CONCLUSION: On the basis of our anecdotal experience and reports by other groups, aggressive treatment with decompression (first rib resection and scalenectomy) and jugular vein transposition could be recommended for persistent subclavian vein thrombosis. Because of the presence of a thoraco-brachial outlet syndrome the endovascular procedures should be completed by first rib resection.

[Coverage of heel tissue loss by two pediculated flaps in a single procedure]. / Couverture d'une perte de substance du talon en un temps par deux lambeaux pédiculés.

We report the case of a traffic accident victim who suffered major tissue loss of the heal. We used two pediculated flaps to close the gap in a single procedure. The remaining tissue presented zones of necrosis from the plantar aspect to the posterior half of the calcaneum, up to the insertion of the calcaneus tendon, extending 5 cm on the posterior aspect of the heal. We decided to combine a medial plantar flap with a lateral supramalleolar flap. The thick medial plantar flap allowed cover of the calcaneum and sensitivity. The calcaneus tendon was covered with the lateral supramalleolar flap. The thickness of the flap was adapted to match the tissue defect. At six months, the patient had recovered walking function with satisfactory weight bearing on the heal. Flap sensitivity was satisfactory with no slipping phenomenon.

[Arthroscopy-guided treatment of fractures of the distal radius: 16 wrists]. / Contrôle arthroscopique dans le traitement des fractures articulaires du radius distal: à propos d'une série de 16 cas.

PURPOSE OF THE STUDY: We report our experience with arthroscopy-guided treatment of fractures of the distal radius. MATERIAL AND METHODS: Between November 2001 and June 2002, 16 patients (10 men, 6 women, mean age 51 years, age range 24-75 years) underwent arthroscopy-guided treatment of articular fractures of the distal radius. Patients were installed with the arm held in a horizontal position with a brace, the wrist under traction. The same procedure was used in all cases: introduction of the arthroscope, joint cleaning and shaving, search for lesions, arthroscopy-guided treatment. Kirschner 2-mm pins were used for fixation in all cases, combined with 1.2-mm pins in the event of ligament injury. RESULTS: Arthroscopic exploration revealed cartilage impaction in 25% of the wrists and ligament injuries in 30%. One fixation disassembled and was not remounted. There were two cases of reflex dystrophy. There were no arthroscopy-related complications. Bone healing was achieved in eight weeks in all cases. The mean DASH score was 22.5 at six months follow-up (range 3-10). DISCUSSION CONCLUSION: Arthroscopy-guided treatment of fractures of the distal radius was attempted for the first time in the early 90s. Per-operative arthroscopy enables a good view of the fracture and associated lesions (cartilage impaction, scapholunate, lunotriquetral ligament injury) and facilitates control of the reduction. Arthroscopy is technically simple and is the technique of choice due to the lack of morbidity. Several authors have reported their experience in more or less extensive series. Two notions should be emphasized. First, defective intra-articular reduction greater than 1 mm may lead to osteoarthritis of the wrist in 90% of the cases. Secondly, intra-operative imaging (fluoroscopy) does not provide sufficient precision to visualize a 1-mm stairstep in the articular surface, raising the risk of radiocarpal degeneration at mid term despite often satisfactory postoperative x-rays. We thus propose intra-operative arthroscopy to control the treatment of all articular wrist fractures, with or without displacement, in order to ensure satisfactory reduction with less than 1-mm defect in the articular surface and to search for and treat any associated bone or ligament injuries not diagnosed before surgery.

The concept of locking plates.

After a short historical review of locking bone plates since their inception more than a century ago to the success of the concept less than 15 years ago with today's plates, the authors present the main locking mechanisms in use. In the two broad categories - plates with fixed angulation and those with variable angulation - the screw head is locked in the plate with a locknut by screwing in a threaded chamber on the plate or by screwing through an adapted ring. The authors then provide a concrete explanation, based on simple mechanical models, of the fundamental differences between conventional bone plates and locking plates and why a locking screw system presents greater resistance at disassembly, detailing the role played by the position and number of screws. The advantages of epiphyseal fixation are then discussed, including in cases of mediocre-quality bone. For teaching purposes, the authors also present assembly with an apple fixed with five locking screws withstanding a 47-kg axial load with no resulting disassembly. The principles of plate placement are detailed for both the epiphysis and diaphysis, including the number and position of screws and respect of the soft tissues, with the greatest success assured by the minimally invasive and even percutaneous techniques. The authors then present the advantages of locking plates in fixation of periprosthetic fractures where conventional osteosynthesis often encounters limited success. Based on simplified theoretical cases, the economic impact in France of this type of implant is discussed, showing that on average it accounts for less than 10% of the overall cost of this pathology to society. Finally, the possible problems of material ablation are discussed as well as the means to remediate these problems.

Thin film growth using hetero embryo: demonstration on pyrochlore phase.

The paper reports the possible use of nanoparticles embedded in amorphous host as hetero embryos in order to grow complex crystalline phases as thin film. Demonstration is performed in the prototypical case of pyrochlore phase Gd(2)Ti(2)O(7) grown from Gd(2)O(3) nanoparticles embedded in TiO(2) matrix at low temperature. As embryos, two kinds of nanoparticles are compared: clusters deposited by low energy cluster beam deposition (LECBD) and nanostructured films elaborated by sol-gel process. The growth has been analyzed by X-ray diffraction and transmission electron microscopy. Furthermore, the nanoparticles have been doped with Eu(3+) luminescence probes in order to follow the nucleation mechanisms at the atomic scale. It is shown that the size, shape, and composition of hetero embryos and as well their interfaces are of paramount importance to enhance the formation of complex materials, such as pyrochlore. By this mean, the first step in classical nucleation science, controlling the height of the energetic barrier, is skipped and the synthesis conditions can be eased.