Quantum dot size dependent influence of the substrate orientation on the electronic and optical properties of InAs/GaAs quantum dots

Using 3D k.p calculation including strain and piezoelectricity we predict variation of electronic and optical properties of InAs/GaAs quantum dots (QDs) with the substrate orientation. The QD transition energies are obtained for high index substrates [11k], where k = 1,2,3 and are compared with [001]. We find that the QD size in the growth direction determines the degree of influence of the substrate orientation: the flatter the dots, the larger the difference from the reference [001] case.Comment: Submitted to Appl. Phys. Let

Optical properties of (In,Ga)As capped InAs quantum dots grown on [11k] substrates

Using three-dimensional k.p calculation including strain and piezoelectricity, we showed that the size of the quantum dot (QD) in the growth direction determines the influence of the (In,Ga)As capping layer on the optical properties of [11k] grown InAs QDs, where k=1,2,3. For flat dots, increase of In concentration in the capping layer leads to a decrease of the transition energy, as is the case of [001] grown QDs, whereas for large dots an increase of the In concentration in the capping layer is followed by an increase of the transition energy up to a critical concentration of In, after which the optical transition energy starts to decrease

Confined states and direction-dependent transmission in graphene quantum wells

We report the existence of confined massless fermion states in a graphene quantum well (QW) by means of analytical and numerical calculations. These states show an unusual quasi-linear dependence on the momentum parallel to the QW: their number depends on the wavevector and is constrained by electron-hole conversion in the barrier regions. An essential difference with non-relativistic electron states is a mixing between free and confined states at the edges of the free-particle continua, demonstrated by the direction-dependent resonant transmission across a potential well.Comment: Submitted to PR

A three-dimensional model for artificial atoms and molecules: Influence of substrate orientation and magnetic field dependence

A full three-dimensional model for the calculation of the electronic structure of semiconductor quantum dots (QD) and molecules (QDM) grown on high index surfaces and/or in the presence of an external magnetic field is presented. The strain distribution of the dots is calculated using continuum elasticity and singe-particle states are extracted from the nonsymmetrized eight-band k.p theory. The model properly takes into account the effects of different substrate orientation by rotation of the coordinate system in the way that one coordinate coincides with the growth direction, whereas the effects of a tilted external magnetic field are taken into account throught the Zeeman effect and employing a gauge invariant scheme based on Wilson's formulation of lattice gauge theory. We point out the role of piezoelectricity for InAs/GaAs QDs grown on [11k], where k = 1,2,3,4,5,7,9 and for QDMs containing eight InAs/GaAs QDs grown on [11l], where l = 1,2,3. We predict the variation of the transition energies of the QDM as a function of substrate orientation and interdot distances in the molecule. We address the magnetic field direction dependent variation of the electronic properties of QD and QDM

The influence of high vitamine c doses on neutrophil granulocytes functions in cows with subclinical masitis

Napredak tehnologije i direktna primena najnovijih nauĉnih saznanja omogućili su, do sada, najvišu produkciju mleka po kravi u farmskim uslovima. Usled intenzivne i jednostrane selekcije na visoku mleĉnost, došlo se do granica biološkog potencijala ove ţivotinjske vrste. Imperativ povećanja proizvodnje (odnosno profita), gde se u velikom broju sluĉajeva, krave iscrpljuju do krajnjih fizioloških granica, nanosi štetu njihovom zdravstvenom stanju uz zanemarivanje osnovnih bioloških principa. Visoko-mleĉne krave se uvode u stanje kontinuiranog metaboliĉkog stresa, koji neminovno rezultira zdravstvenim i proizvodnim problemima. Indirektno se, kao posledica narušavanja imunološkog statusa jedinki, pojavljuje najvaţniji zdravstveni i ekonomski problem u mleĉnom govedarstvu, a to je upala mleĉne ţlezde - mastitis. Štete u vidu smanjene proizvodnje ĉine preko 70% svih gubitaka produkcije mleka, dok leĉenje mastitisa ĉini preko 50% svih intervencija na farmama mleĉnih krava. Posebno treba naglasiti ĉinjenicu da se najveći deo problema u realnim uslovima proizvodnje odnosi na supkliniĉke mastitise, koji nisu direktno vidljivi i oni dovode do najvećih finansijskih gubitaka. Zbog toga su farme bez adekvatnog programa mera kontrole i suzbijanja supkliniĉkog mastitisa, zapati sa ugroţenim opstankom. Smatra se da se fiziološke potrebe odraslih preţivara u vitaminu C obezbeĊuju aktivnošću bakterijske mikroflore buraga. Vitamin C nije esencijalan dijetalni dodatak u ishrani odraslih preţivara. MeĊutim, istovremeno je dokazano da se zdravstveno stanje organizma preţivara poboljšava kada se vitamin C dodaje u hranu u uslovima stresa ili bolesti. TakoĊe je poznato da oralna aplikacija nije toliko efikasna kao parenteralna. Rana laktacija predstavlja najkritiĉniji period reproduktivno-proizvodnog ciklusa, kada se mobilišu gotovo svi raspoloţivi fiziološki resursi i tada dolazi do pada koncentracije askorbinske kiseline u krvnoj plazmi mleĉnih krava. Istovremeno se od mleĉnih krava oĉekuje oporavak od teljenja, postizanje vrhunske mleĉnosti i novog graviditeta u što kraćem vremenskom periodu. Postoje podaci koji dokazuju da je i tokom supkliniĉkog, a pogotovo kliniĉkog mastitisa izraţen pad koncentracije vitamina C u krvnoj plazmi plotkinja. Shodno tome, osnova ovog istraţivanja je bila zasnovana na pretpostavci da se poboljšanje opšte otpornosti organizma stimulacijom funkcija neutrofilnih granulocita (stepena fagocitoze i respiratornnog praska) kao prve linije odbrane od infekcija, moţe postići produţenom aplikacijom visokih doza vitamina C, višestruko većim od farmakološki preporuĉenih. Kliniĉki su oĉekivani pozitivni efekti na smanjenje broja somatskih ćelija u mleku i poboljšanje ukupnog zdravstvenog i reproduktivnog statusa. Sa druge strane, ne postoje dostupni podaci o toksiĉnosti vitamina C kod preţivara prekomernim doziranjem. Ciljevi ovog istraţivanja su bili da se utvrdi uticaj visokih doza vitamina C na kvalitet mleka ocenjen CMT (California Mastitis Test), 10 do 30 dana posle teljenja, pre i nakon tretmana vitaminom C (tretirana grupa), odnosno, na poĉetku i na kraju ogleda u kontrolnoj grupi (bez tretmana). Osim toga ispitan je bakteriološki nalaz mleka iz CMT pozitivnih ĉetvrti na poĉetku i na kraju ogleda, u zavisnosti od tretmana vitaminom C. Kod svih jedinki, ukljuĉenih u ogled odreĊivane su kompletna krvna sliku i leukogram, pre i nakon tretmana vitaminom C. Na kraju je utvrĊivan stepen funkcionalne aktivnosti neutrofilnih granulocita (intenzitet fagocitoze i repiratornog praska) u punoj krvi i mleku krava u navedenom periodu. U ispitivanja je bilo ukljuĉeno 40 grla, odabranih prema sledećim kriterijumima: 1) da je od teljenja prošlo najmanje 10 a ne više od 30 dana; 2) da je na jutarnjoj muţi mleko krava ispoljavalo pozitivnu reakciju u CMT (sa ++ i +++ reakcijom) u jednoj ili više ĉetvrti, bez kliniĉki vidljivog mastitisa; 3) da je zapis toka teljenja bio normalan, bez dodatne asistencije akušera; 4) da su odabrane krave kliniĉki bile zdrave...Development of new technologies and direct application of the latest scientific findings enabled the highest milk production per cow ever in farm conditions. Due to the intense and narrow selection for high milk yield today, we approached the limits of the biological potential of this species. The imperative of increased production (or profit), where in a good number of cases cows are exhausted to the extreme physiological limits in order to achieve greater milk production, harming their health status and fully neglecting basic biological principles. In this way, we are introducing them into a state of continuous stress, which inevitably results in a wide range of health and/or production problems. Indirectly, as a result of disturbance of the immune status, the most important health and economic problem within dairy cattle production, appears inflammation of the mammary gland - mastitis. The damage in terms of reduced milk production account for over 70% of all milk production losses, while treating mastitis comprise over 50% of all interventions on dairy farms. We should emphasize the fact that the biggest part of the problem in real production conditions is related to subclinical mastitis, which is not directly visible. The real fact is that subclinical mastitis brings the largest financial losses. A farm without adequate program of measures to control and combat subclinical mastitis doesn’t have “bright” future. It is believed that sufficient physiological needs of adult ruminants in vitamin C are provided by activity of the rumen bacterial microflora. Also, it is believed that vitamin C is not essential dietary nutrient in the diet of adult ruminants, but their body condition are improved when they had vitamin C added to the diet in situation of stress or illness. Also, oral application is not as effective as the parenteral route. After calving, in its early phase of lactation there is a decrease in concentration of ascorbic acid (vitamin C) in the blood plasma of dairy cows. Early lactation represents the most critical period of reproductive-production cycle, when almost all available physiological resources are mobilized and pushed to the final limits. The dairy cows are expected to recover from calving, reaching soon the peak of lactation and a new pregnancy in the shortest possible time. The decrease in the concentration of vitamin C is expressed during subclinical, especially during clinical mastitis. Consequently, the platform of this research is based on the assumption that an improvement in the general resistance of the organism by stimulating the neutrophil granulocytes (phagocytosis and respiratory burst) as a first line of defence against infection can be achieved by prolonged application of high vitamin C doses, a multiple higher than the pharmacologically recommended. Clinically, the expected positive effects are the reduction of somatic cells in milk and improved overall health and reproductive status. On the other hand, there are no available data on the toxicity of vitamin C in ruminants excessive dosing. The main objectives of this study were: to determine the effect of high doses of vitamin C on the quality of milk, estimated with CMT test; 10 to 30 days after calving, before and after treatment with vitamin C (experimental group), respectively, at the beginning and end of the experiment in the control group (no treatment); to perform milk bacteriological examination of CMT positive udder quarters at the beginning and end of the trial, depending on the treatment of vitamin C; to determine complete blood count and leukogram in cows before and after the treatment with vitamin C; to determine degree of functional activity of neutrophil granulocytes (phagocytosis and respiratory burst) from whole blood and CMT positive milk samples (++, +++) in the related period (before and after the treatment). Fourty cows has been selected, according to the following selection criteria: 1) from the calving has passed at least 10 days and not more than 30 days; 2) at the morning milking cows milk produced positive reaction to the CMT (with ++ and +++ reaction) from one or more udder quarters, without clinically apparent mastitis; 3) the calving was normal, without additional assistance of veterinarian; 4) selected cows had to be clinically healthy..

Anisotropic Confinement, Electronic Coupling and Strain Induced Effects Detected by Valence-Band Anisotropy in Self-Assembled Quantum Dots

A method to determine the effects of the geometry and lateral ordering on the electronic properties of an array of one-dimensional self-assembled quantum dots is discussed. A model that takes into account the valence-band anisotropic effective masses and strain effects must be used to describe the behavior of the photoluminescence emission, proposed as a clean tool for the characterization of dot anisotropy and/or inter-dot coupling. Under special growth conditions, such as substrate temperature and Arsenic background, 1D chains of In0.4Ga0.6 As quantum dots were grown by molecular beam epitaxy. Grazing-incidence X-ray diffraction measurements directly evidence the strong strain anisotropy due to the formation of quantum dot chains, probed by polarization-resolved low-temperature photoluminescence. The results are in fair good agreement with the proposed model

Electro-elastic tuning of single particles in individual self-assembled quantum dots

We investigate the effect of uniaxial stress on InGaAs quantum dots in a charge tunable device. Using Coulomb blockade and photoluminescence, we observe that significant tuning of single particle energies (~ -0.5 meV/MPa) leads to variable tuning of exciton energies (+18 to -0.9 micro-eV/MPa) under tensile stress. Modest tuning of the permanent dipole, Coulomb interaction and fine-structure splitting energies is also measured. We exploit the variable exciton response to tune multiple quantum dots on the same chip into resonance.Comment: 16 pages, 4 figures, 1 table. Final versio

High resolution nuclear magnetic resonance spectroscopy of highly-strained quantum dot nanostructures

Much new solid state technology for single-photon sources, detectors, photovoltaics and quantum computation relies on the fabrication of strained semiconductor nanostructures. Successful development of these devices depends strongly on techniques allowing structural analysis on the nanometer scale. However, commonly used microscopy methods are destructive, leading to the loss of the important link between the obtained structural information and the electronic and optical properties of the device. Alternative non-invasive techniques such as optically detected nuclear magnetic resonance (ODNMR) so far proved difficult in semiconductor nano-structures due to significant strain-induced quadrupole broadening of the NMR spectra. Here, we develop new high sensitivity techniques that move ODNMR to a new regime, allowing high resolution spectroscopy of as few as 100000 quadrupole nuclear spins. By applying these techniques to individual strained self-assembled quantum dots, we measure strain distribution and chemical composition in the volume occupied by the confined electron. Furthermore, strain-induced spectral broadening is found to lead to suppression of nuclear spin magnetization fluctuations thus extending spin coherence times. The new ODNMR methods have potential to be applied for non-invasive investigations of a wide range of materials beyond single nano-structures, as well as address the task of understanding and control of nuclear spins on the nanoscale, one of the central problems in quantum information processing

Acute effects of MDMA (3,4-methylenedioxymethamphetamine) on EEG oscillations: alone and in combination with ethanol or THC (delta-9-tetrahydrocannabinol)

Item does not contain fulltextRATIONALE: Typical users of 3,4-methylenedioxymethamphetamine (MDMA or "ecstasy") are polydrug users, combining MDMA with alcohol or cannabis [most active compound: delta-9-tetrahydrocannabinol (THC)]. OBJECTIVES: The aim of the present study was to investigate whether co-administration of alcohol or THC with MDMA differentially affects ongoing electroencephalogram (EEG) oscillations compared to the administration of each drug alone. METHODS: In two separate experiments, 16 volunteers received four different drug conditions: (1) MDMA (100 mg); (2) alcohol clamp (blood alcohol concentration = 0.6 per thousand) or THC (inhalation of 4, 6 and 6 mg, interval of 1.5 h); (3) MDMA in combination with alcohol or THC; and (4) placebo. Before and after drug administration, electroencephalography was recorded during an eyes closed resting state. RESULTS: Theta and alpha power increased after alcohol intake compared to placebo and reduced after MDMA intake. No interaction between alcohol and MDMA was found. Significant MDMA x THC effects for theta and lower-1-alpha power indicated that the power attenuation after the combined intake of MDMA and THC was less than the sum of each drug alone. For the lower-2-alpha band, the intake of MDMA or THC alone did not significantly affect power, but the intake of combined MDMA and THC significantly decreased lower-2-alpha power. CONCLUSIONS: The present findings indicate that the combined intake of MDMA and THC, but not of MDMA and alcohol, affects ongoing EEG oscillations differently than the sum of either one drug alone. Changes in ongoing EEG oscillations may be related to the impaired task performance that has often been reported after drug intake