Effects of Dislocation Filtering Layers on Optical Properties of Third Telecom Window Emitting InAs/InGaAlAs Quantum Dots Grown on Silicon Substrates.

Integrating light emitters based on III-V materials with silicon-based electronics is crucial for further increase in data transfer rates in communication systems since the indirect bandgap of silicon prevents its direct use as a light source. We investigate here InAs/InGaAlAs quantum dot (QD) structures grown directly on 5° off-cut Si substrate and emitting light at 1.5 µm, compatible with established telecom platform. Using different dislocation defect filtering layers, exploiting strained superlattices, and supplementary QD layers, we mitigate the effects of lattice constant and thermal expansion mismatches between III-V materials and Si during growth. Complementary optical spectroscopy techniques, i.e. photoreflectance and temperature-, time- and polarization-resolved photoluminescence, allow us to determine the optical quality and application potential of the obtained structures by comparing them to a reference sample-state-of-the-art QDs grown on InP. Experimental findings are supported by calculations of excitonic states and optical transitions by combining multiband k•p and configuration-interaction methods. We show that our design of structures prevents the generation of a considerable density of defects, as intended. The emission of Si-based structures appears to be much broader than for the reference dots, due to the creation of different QD populations which might be a disadvantage in particular laser applications, however, could be favorable for others, e.g., in broadly tunable devices, sensors, or optical amplifiers. Eventually, we identify the overall most promising combination of defect filtering layers and discuss its advantages and limitations and prospects for further improvements.

Diagnosis of Coronary Stent Dislodgement With Transthoracic Echocardiogram: A Case Report.

Coronary stent dislodgment is a rare complication of percutaneous coronary intervention (PCI). Although stent dislodgment typically occurs immediately in the intraoperative or perioperative period, it can infrequently occur subacutely in the post-operative period. Diagnosis of stent dislodgment can be seen with various cardiac imaging modalities, from transthoracic and transesophageal echocardiogram to cardiac computed tomography or magnetic resonance imaging to direct visualization on fluoroscopy during cardiac catheterization. Given the rarity of this entity, there is a lack of established common practice, gold standard for treatment, and/or procedural data. Instances are managed on a case-by-case basis, using the imaging modalities readily available at the institution and treatment modalities the interventionalist or surgeon is most comfortable with. Therefore, management of stent dislodgment consists of conservative, percutaneous, or surgical interventions on a case-by-case basis. We present a case of right coronary artery stent migration that was incidentally diagnosed with routine transthoracic echocardiogram.

Electronic and magnetic properties of 2D vanadium-based transition metal dichalcogenides.

In this paper, electronic and magnetic properties of monolayers and bilayers of Vanadium-based transition metal dichalcogenides VX2 (X = S, Se, Te) in the H phase are investigated theoretically using methods based on DFT calculations as well as analytical methods based on effective spin Hamiltonians. The band structure has been computed for all systems, and then the results have been used to determine exchange parameters and magnetic anisotropy constants. These parameters are subsequently used for the determination of the Curie temperatures, hysteresis curves, and energy of spin-wave excitations. In the latter case, we compare analytical results based on effective spin Hamiltonian with those determined numerically by Quantum ATK software and find a good agreement. The determined Curie temperature for VTe2 monolayers and bilayers is below the room temperature (especially that for bilayers), while for the other two materials, i.e. for VS2 and VSe2, it is above the room temperature, in agreement with available experimental data.

Temperature dependence of refractive indices of Al0.9Ga0.1As and In0.53Al0.1Ga0.37As in the telecommunication spectral range.

In this work, we determine the temperature dependence of refractive indices of In0.53Al0.1Ga0.37As and Al0.9Ga0.1As semiconductor alloys at telecommunication wavelengths in the range from room temperature down to 10 K. For that, we measure the temperature-dependent reflectance of two structures: with an Al0.9Ga0.1As/GaAs distributed Bragg reflector (DBR) designed for 1.3 µm and with an In0.53Al0.1Ga0.37As/InP DBR designed for 1.55 µm. The obtained experimental results are compared to DBR reflectivity spectra calculated within the transfer matrix method to determine refractive index values. We further show that changes due to the thermal expansion of the DBR layers are negligible for our method.

Magneto-Optical Characterization of Trions in Symmetric InP-Based Quantum Dots for Quantum Communication Applications.

Magneto-optical parameters of trions in novel large and symmetric InP-based quantum dots, uncommon for molecular beam epitaxy-grown nanostructures, with emission in the third telecom window, are measured in Voigt and Faraday configurations of an external magnetic field. The diamagnetic coefficients are found to be in the range of 1.5-4 µeV/T2, and 8-15 µeV/T2, respectively out-of-plane and in-plane of the dots. The determined values of diamagnetic shifts are related to the anisotropy of dot sizes. Trion g-factors are measured to be relatively small, in the range of 0.3-0.7 and 0.5-1.3, in both configurations, respectively. Analysis of single carrier g-factors, based on the formalism of spin-correlated orbital currents, leads to similar values for hole and electron of ~0.25 for Voigt and ge ≈ -5; gh ≈ +6 for Faraday configuration of the magnetic field. Values of g-factors close to zero measured in Voigt configuration make the investigated dots promising for electrical tuning of the g-factor sign, required for schemes of single spin control in qubit applications.

Carrier transfer efficiency and its influence on emission properties of telecom wavelength InP-based quantum dot - quantum well structures.

We investigate a hybrid system containing an In0.53Ga0.47As quantum well (QW), separated by a thin 2 nm In0.53Ga0.23Al0.24As barrier from 1.55 µm emitting InAs quantum dots (QDs), grown by molecular beam epitaxy on an InP substrate. Photoreflectance and photoluminescence (PL) spectroscopies are used to identify optical transitions in the system, with support of 8-band kp modelling. The main part of the work constitute the measurements and analysis of thermal quenching of PL for a set of samples with different QW widths (3-6 nm). Basing on Arrhenius plots, carrier escape channels from the dots are identified, pointing at the importance of carrier escape into the QW. A simple two level rate equations model is proposed and solved, exhibiting qualitative agreement with experimental observations. We show that for a narrow QW the escape process is less efficient than carrier supply via the QW due to the narrow barrier, resulting in improved emission intensity at room temperature. It proves that with carefully designed energy level structure, a hybrid QW/QD system can be used as an active region in telecom lasers with improved efficiencies.

Brain ischemia in patients with intracranial hemorrhage: pathophysiological reasoning for aggressive diagnostic management.

Patients with intracranial hemorrhage have to be managed aggressively to avoid or minimize secondary brain damage due to ischemia, which contributes to high morbidity and mortality. The risk of brain ischemia, however, is not the same in every patient. The risk of complications associated with an aggressive prophylactic therapy in patients with a low risk of brain ischemia can outweigh the benefits of therapy. Accurate and timely identification of patients at highest risk is a diagnostic challenge. Despite the availability of many diagnostic tools, stroke is common in this population, mostly because the pathogenesis of stroke is frequently multifactorial whereas diagnosticians tend to focus on one or two risk factors. The pathophysiological mechanisms of brain ischemia in patients with intracranial hemorrhage are not yet fully elucidated and there are several important areas of ongoing research. Therefore, this review describes physiological and pathophysiological aspects associated with the development of brain ischemia such as the mechanism of oxygen and carbon dioxide effects on the cerebrovascular system, neurovascular coupling and respiratory and cardiovascular factors influencing cerebral hemodynamics. Consequently, we review investigations of cerebral blood flow disturbances relevant to various hemodynamic states associated with high intracranial pressure, cerebral embolism, and cerebral vasospasm along with current treatment options.

Use of antiplatelet agents in patients with atherosclerotic disease.

Platelets play a key role in the initiation of hemostatic mechanisms during vascular injury. When contemplating prescription of antiplatelet agents (APAs) for patients as primary prevention for cardiovascular events, the physician should carefully weigh the potential benefits of cardiovascular risk reduction with the likelihood of harm, related mostly to hemorrhagic complications. The role of APAs in secondary prevention of atherosclerosis and coronary artery disease is well established, however, optimal duration of therapy and intensity of patient treatment are not settled and probably need to be individualized per patient. We describe the data emerging from contemporary trials on the efficacy and safety of the use of oral APAs in various patient subpopulations. We also discuss the advantages and potential roles of new APAs during and following acute coronary syndromes, percutaneous coronary interventions, and symptomatic atherosclerosis. We propose certain strategies and directions for future research to enhance the safety and efficacy prevention by optimizing the beneficial effects of APAs along with other contemporary treatment modalities of primary and secondary prevention.

Comparison of efficacy and safety of intracoronary sodium nitroprusside and intravenous adenosine for assessing fractional flow reserve.

OBJECTIVES: The purpose of this study was to compare the efficacy and safety of intracoronary (IC) nitroprusside and intravenous adenosine (IVA) for assessing fractional flow reserve (FFR). BACKGROUND: IV infusion of adenosine is a standard method to achieve a coronary hyperemia for FFR measurement. However, adenosine is expensive, causes multiple side effects, and is contraindicated in patients with reactive airway disease. Sodium nitroprusside (NTP) is a strong coronary vasodilator but its efficacy and safety for assessing FFR is not well established. METHODS: We compared FFR response and side effects profile of IC NTP and IVA. Bolus of NTP at a dose of 100 µg and IVA (140 µg/kg/min) were used to achieve coronary hyperemia. RESULTS: We evaluated 75 lesions in 53 patients (60% male) mean age 61.6 ± 13.9 years. Mean FFR after NTP was similar to FFR after adenosine (0.836 ± 0.107 vs. 0.856 ± 0.106; P = 0.26; r = 0.91, P < 0.001). NTP induced maximal stable hyperemia within 10 sec (mean: 6.4 ± 1) which lasted consistently between 38 and 60 sec (mean 51 ± 7.5). NTP caused significant (14%), but asymptomatic decrease in mean blood pressure which returned to baseline within 60 sec. Adenosine caused shortness of breath in 26%, headache and flushing in 19%, and transient second degree heart block in 6% of patients. No adverse symptoms were reported after NTP. CONCLUSIONS: IC NTP is as effective as IVA for measuring FFR. NTP is better tolerated by patients. Since NTP is inexpensive, readily available, well tolerated, and safe, it may be a better choice for FFR assessment.

New index for assessing the chronotropic response in patients with end-stage liver disease who are undergoing dobutamine stress echocardiography.

The inability to achieve 85% of the maximum predicted heart rate (MPHR) on dobutamine stress echocardiography (DSE) is defined as chronotropic incompetence and is a predictor of major cardiac events after orthotopic liver transplantation (OLT). The majority of patients with end-stage liver disease (ESLD) receive beta-blockers for the prevention of variceal bleeding. In these patients, it is impossible to determine whether chronotropic incompetence is secondary to cirrhosis-related autonomic dysfunction or is merely a beta-blocker effect. We evaluated the usefulness of the maximum achieved heart rate (MAHR) and the heart rate reserve (HRR) in the detection of chronotropic incompetence in ESLD patients on beta-blocker therapy before DSE. We also evaluated the usefulness of a new index, the modified heart rate reserve (MHRR), in diagnosing chronotropic incompetence and predicting major cardiovascular adverse events after OLT. The study population consisted of 284 ESLD patients. The mean values of MAHR (expressed as a percentage of 85% of MPHR) and HRR were significantly lower for patients on beta-blockers versus patients off beta-blockers [97.1% versus 101.6% (t = 5.01, P < 0.001) and 71.7% versus 77.3% (t = 4.03, P < 0.001), respectively], whereas the values of MHRR were similar in patients on beta-blockers and patients off beta-blockers [102.3% versus 102.1% (t = 0.04, P = 0.97)]. A regression analysis showed a significant association of MAHR (P < 0.001) and HRR (P < 0.001) with beta-blockers, whereas MHRR was not associated with beta-blocker treatment (P = 0.92). MAHR and HRR were found to have no value for diagnosing chronotropic incompetence in ESLD patients. MHRR was not affected by beta-blocker therapy. Patients who developed heart failure (HF) and myocardial infarction (MI) after OLT had significantly lower MHRR values according to pretransplant DSE. MHRR was significantly associated with the subsequent development of HF (P = 0.01) and MI (P = 0.01) after OLT. MHRR may be useful for the determination of the target heart rate for stress testing, the diagnosis of chronotropic incompetence, and the prediction of adverse cardiac events after OLT.

Sickle cell disease: ratio of blood flow velocity of intracranial to extracranial cerebral arteries--initial experience.

PURPOSE: To establish reference values of the ratios of flow velocity in the middle cerebral artery (V(MCA)) and the terminal portion of the internal carotid artery (V(tICA)) to flow velocity in the extracranial portion of internal carotid artery (V(ICA)) in children with sickle cell disease (SCD). MATERIALS AND METHODS: Institutional ethics committee approval and parental informed consent were obtained for this prospective HIPAA-compliant study. Sixty-eight children (38 female; mean age, 7.7 years +/- 3.3; range, 2-14 years) with HbSS genotype, without neurologic deficits and no history of stroke, were enrolled. Final study population comprised 56 (mean age 8.0 +/- 3.3 years, 26 females) children who underwent magnetic resonance (MR) angiography, which excluded intracranial arterial narrowing, transcranial color-coded duplex ultrasonography (US), and carotid US to determine V(MCA)/V(ICA) and V(tICA)/V(ICA) ratios from angle-corrected and uncorrected velocities. Tolerance interval estimates were used to calculate reference ranges and linear regression was used to quantify associations of Doppler parameters with age adjusted for hemoglobin and hematocrit. RESULTS: Reference ranges in centimeters per second for mean angle-corrected V(MCA) on the left and right sides were 62-198 and 69-153; those for V(tICA) were 30-196 and 36-175; and those for V(ICA) were 18-116 and 15-95, respectively. Reference ranges for mean angle-corrected V(MCA)/V(ICA) ratio on the left and right sides were 1.2-4.0 and 0.4-3.4 and those for V(tICA)/V(IC)(A) ratio were 0.5-2.9 and 0.5-2.7, respectively. V(MCA), V(tICA), and V(tICA)/V(ICA) ratio were not age dependent, contrary to V(ICA) and V(MCA)/V(ICA) ratio, after controlling for hematocrit and hemoglobin. CONCLUSION: The study provides reference limits for V(MCA), V(tICA), V(ICA), and velocity ratios obtained from children with SCD.

Cerebral hemodynamics and investigations of cerebral blood flow regulation.

To maintain adequate cerebral blood flow despite frequent changes in systemic arterial blood pressure and to constantly adjust blood supply to the current metabolic demand dictated by neuronal electrical activity, brain developed a myriad of mechanisms. These are designed to protect central nervous system from fatal consequences of hypoxia and energy deficit and are collectively called "cerebral autoregulation". Despite years of research mechanisms responsible for regulation of CBF functioning under physiologic and pathologic conditions are still not clear. When these mechanisms are damaged or exhausted, patients life is in danger, as even slight, negligible under normal conditions, systemic hemodynamic disturbances might lead to cerebral infarct. Even perfect imaging of the irreversible brain damage with MR for the particular patient is too late action. Thus, detection of cerebral blood flow disturbances and impaired autoregulation, which are known to be associated with high risk of stroke, are extremely important in clinical practice. Several methods have been developed to quantify this process and thus evaluate risk of cerebral ischemia and guide therapeutic process. This review focuses on current knowledge on physiology of regulation of cerebral blood flow, mechanisms responsible for brain damage resulted from cerebral ischemia and reviews noninvasive diagnostic tests to assess cerebral autoregulation.

[Hypothermia as a neuroprotective agent]. / Hipotermia jako czynnik neuroprotekcyjny.

Hypothermia has long been employed for therapeutic purposes but its use has been limited because of the potential life-threatening side-effects. In late eighties a neuroprotective effect of bold hypothermia was demonstrated and this implied that the method could be used more safely. It has then been shown in a lot of animal experiments that post-ischaemic mild hypothermia significantly limits damage to the brain caused by cardiac arrest. Similar results have been obtained for local brain ischaemia and for experimental head trauma. Molecular basis for this neuroprotection with mild hypothermia has been found to be complex, involving attenuation of the excitotoxic effects of glutamate and diminishing the synthesis of free radicals. In the last decade some clinical series and multicenter randomised trials have shown that mild hypothermia is safe and effective in global brain ischaemia due to cardiac arrest. Clinical data suggest also its effectiveness in ischaemic stroke though no multicenter randomised study has been published to date. At present there are conflicting results of clinical trials concerning brain injuries. Although some authors have reported up to 38% improvement in the outcome, a recently published multicenter randomised trial has failed to demonstrate any practical benefit of mild hypothermia after acute brain injury. There is however virtually no data in the literature on mild hypothermia in spinal cord injury.

[Transcranial color Doppler sonography (TCCD) in the diagnosis of vasospasm in the middle cerebral artery. Evaluation of TCCD diagnostic effectiveness by means of receiver operating characteristics curve (ROC) analysis]. / Przezczaszkowa ultrasonografia dopplerowska z kolorowym odwzorowaniem przeplywu w rozpoznawaniu skurczu tetnicy srodkowej mózgu. Ocena skutecznosci diagnostycznej za pomoca krzywej charakterystyki odbiornika.

Transcranial Doppler sonography is commonly used for diagnosis of cerebral vasospasm. However, the overall diagnostic performance of this method in detection of arterial narrowing has not been established. Blood velocity threshold, diagnostic for vasospasm, has been proposed for conventional, "blind" transcranial Doppler sonography (TCD). Nevertheless it cannot be used for transcranial color Doppler sonography (TCCD), because in this method the obtained blood velocities in the major cerebral arteries are higher than are in TCD. The aim of this study was to estimate the accuracy of transcranial color Doppler sonography in detection of middle cerebral artery (MCA) narrowing by means of receiver operating characteristic curve analysis (ROC). One hundred thirty four patients were studied with TCCD immediately before cerebral angiography. There were 75 men and 59 women, age range from 18 to 74 years, mean age 49 years. Of the 268 MCAs examined, 227 arteries were finally included in the construction of the ROC curve. Angiographic vasospasm was graded as none, mild (equal to or less than 25% of vessel caliber reduction--16 patients) and moderate-to-severe (more than 25% of vessel caliber reduction--29 patients). The overall diagnostic performance of transcranial color Doppler sonography in the detection of moderate-to-severe vasospasm of middle cerebral artery was found to be very high. The value of associated area under the ROC curve was 0.94. The value of this area for all vasospasms was 0.85, and this indicates good accuracy of a test. The best performing TCCD parameter for the detection of MCA narrowing was revealed to be peak-systolic velocity. The optimal trade-off between sensitivity and specificity was achieved with a peak systolic velocity of 182 cm/s. Therefore this velocity threshold is proposed as most universal for the diagnosis of vasospasm in the middle cerebral artery.

[Effects of estrogens on the brain and implications for neuro-protection]. / Oddzialywanie estrogenów na mózg ze szczególnym uwzglednieniem dzialania neuroprotekcyjnego.

Numerous biological effects of oestrogens within the brain support the argument that their influence is not restricted to the reproductive system. Specific estrogen receptors were found in the central nervous system as early as in the 70's, but until recently little was known about the molecular background of oestrogens activity in the brain. The last decade witnessed a great effort aimed at better understanding of the tangled molecular mechanisms underlying subtle liaisons between brain metabolism and cerebral blood flow and particularly their disturbances triggered by brain ischaemia. These investigations had an ultimate goal--an effective method of preventing an expanding biochemical "catastrophe" within and around the ischaemic brain regions (the so-called "neuroprotection"). Molecular mechanisms by which oestrogens increase both metabolism and blood flow through certain regions of the brain became only recently better understood. Now there is a consensus as to that these hormones increase secretion of neuromediators, stimulate formation of new synapses and can activate certain genes, responsible for production of anti-apoptotic proteins and growth factors. Oestrogens can also dilate cerebral vessels, here acting through increased synthesis of nitric oxide and by stimulating such compounds as prostacycline and a potent vasodilator-epoxyeikosotrienoic acid. There is a body of recent evidence which suggest that during brain ischaemia the physiological estrogen stimulation, of both, brain metabolism and cerebral blood flow, becomes biased towards increased release of vasodilating substances. As the metabolism is not spurred accordingly, the net effect of oestrogens is neuroprotection. Other protective properties of oestrogens within the brain are related to attenuation of the excitotoxic effects of glutamate and to the activation of enzymes scavenging free oxygen radicals. Moreover, oestrogens can diminish free radicals synthesis and act as free radicals scavengers themselves. They can also activate synthesis of bcl-2 protein, which prevents cell apoptosis in the ischaemic regions. The relevant evidence, which continue to accumulate, may suggest that it is time now to consider launching a clinical investigation on the role of oestrogens as potentially important neuroprotective factors.