Search results for " Gai"
showing 10 items of 446 documents
Superluminal two-color light in multiple Raman gain medium
2014
We investigate theoretically the formation of two-component light with superluminal group velocity in a medium controlled by four Raman pump fields. In such an optical scheme only a particular combination of the probe fields is coupled to the matter and exhibits superluminal propagation, the orthogonal combination is uncoupled. The individual probe fields do not have a definite group velocity in the medium. Calculations demonstrate that this superluminal component experiences an envelope advancement in the medium with respect to the propagation in vacuum.
Active reduction of fluctuations in fourth-order modulation instability
2012
International audience; We experimentally study the fluctuation properties of a scalar fourth-order modulation instability process obtained by pumping a photonic crystal fiber in the normal dispersion region. We observe large wavelength-dependant pulse-to-pulse fluctuations which cannot be significantly reduced by stimulating the process with a single seed. Their reduction requires two seeds slightly detuned from the maximum gain frequency in order to also stimulate the second-order modulation instability process cascaded from the fourth-order one. This concept is validated by experiments and numerical simulations.
Preliminary radiation hardness tests of single photon Si detectors
2010
Single photon Si detectors were fabricated by STMicroelectronics and fully characterized in standard operation conditions and after irradiations. Both single cells and arrays, of dimensions ranging from 5x5 up to 64x64, were electrically tested. The devices operation was studied as a function of the temperature from -25 degrees C to 65 degrees C varying the voltage over breakdown, from 5% up to 20% of the breakdown voltage before and after irradiation using both light ions, 10 MeV B ions to doses in the range 3x10(7)-5x10(10) cm(-2), and X-rays irradiations in the range 0.5-20 krad(Si). Optical characterization was performed using a laser at 659 nm and opportunely chosen filters to vary the…
Vecāku iesaiste 3-4 gadus vecu bērnu fizisko aktivitāšu organizēšanā
2018
Kvalifikācijas darba autore: Dana Augustova Darba nosaukums: Vecāku iesaiste 3-4 gadus vecu bērnu fizisko aktivitāšu organizēšanā Darba mērķis: Veicināt vecāku iesaisti 3-4 gadus vecu bērnu fizisko aktivitāšu organizēšanā. Bērna fiziskā attīstība ir ļoti būtiska turpmākā bērna attīstības procesā. Mūsdienās ar straujo tehnoloģiju attīstību, ar vecāku aizņemtību, tiek aizmirsts par bērna iekšējo vajadzību nepieciešamību „kustēties”. Mūsdienu gadsimta bērniem vecāku iesaistīšanās fizisko aktivitāšu organizēšanā ir nepieciešama vairāk nekā jebkad, jo daudzie raksti, grāmatas, apkārtējo viedokļi, kā arī novērojumi liecina par to, ka mūsdienu bērni kļūst aizvien mazkustīgāki. Pats biedējošākais i…
Optimal Design of an X-Band, Fully-Coaxial, Easily-Tunable Broadband Power Equalizer for a Microwave Power Module
2020
A microwave power module (MPM), which is a hybrid combination of a solid-state power amplifier (SSPA) as a driver and a traveling-wave tube amplifier (TWT) as the final high power stage, is a high-power device largely used for radar applications. A gain equalizer is often required to flatten the TWT output power gain owing to its big gain fluctuations over the operating frequency range. In this paper, the design of an X-band, fully-coaxial, easily-tunable broadband power equalizer for an MPM is presented. The structure is composed of a coaxial waveguide as the main transmission line and a coaxial cavity loaded with absorbing material as a resonant unit. Sensitivity analyses of the attenuati…
VECĀKĀ PIRMSSKOLAS VECUMA BĒRNAM NEPIECIEŠAMĀS PRASMES VEIKSMĪGU SKOLAS GAITU UZSĀKŠANAI
2017
Vita Numceva. Bakalaura darbs. Vecāka pirmsskolas vecuma bērnam nepieciešamās prasmes veiksmīgu skolas gaitu uzsākšanai. Latvijas Universitāte, 2017 Bakalaura darba mērķis ir veikt pētījumu par vecākā pirmsskolas vecuma bērnam nepieciešamajām prasmēm, lai veiksmīgi uzsāktu skolas gaitas. Pētījuma gaita un tā rezultāti izklāstīti 2 nodaļās. Pirmā nodaļā tiek analizētas teorētiskās atziņas par bērnam nepieciešāmajām kompetencēm, lai veiksmīgi uzsāktu skolas gaitas, raksturoti bērni vecākajā pirmsskolas vecumā pētāma temata aspektā un izpētīti faktori, kas ietekmē bērna gatavību mācībām skolā. Otrā nodaļa veltīta pētījuma metodoloģijas izstrādēi un veikts pētījums pirmsskolas izglītības iestād…
Size dependent light absorption modulation and enhanced carrier transport in germanium quantum dots devices
2015
Quantum confinement in closely packed arrays of Ge quantum dots (QDs) was studied for energy applications. In this work, we report an efficient tuning mechanism of the light harvesting and detection of Ge QDs. Thin films of SiGeO alloys, produced by rf-magnetron sputtering, were annealed at 600 degrees C in N-2 to induce precipitation of small amorphous Ge QDs into the oxide matrix. Varying the Ge content, the QD size was tailored between 2 and 4 nm, as measured by high resolution transmission electron microscopy. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of pure SiO2, as well as the presence of a sub-stoichiometric Ge oxide shell at the QD interface. Light …
A Smartphone App to Promote Healthy Weight Gain, Diet, and Physical Activity During Pregnancy (HealthyMoms): Protocol for a Randomized Controlled Tri…
2019
Background: Excessive gestational weight gain is common and associated with adverse outcomes both in the short and long term. Although traditional lifestyle-based interventions have shown to mitigate excess gestational weight gain, little is known about whether mobile Health (mHealth) apps can promote healthy weight gain, diet, and physical activity during pregnancy. Objective: The primary aim of the HealthyMoms trial is to determine the effectiveness of a smartphone app (HealthyMoms) for mitigating excess gestational weight gain during pregnancy. Secondary aims are to determine the effectiveness of the app on dietary habits, physical activity, body fatness, and glycemia during pregnancy. M…
The human milk microbiome changes over lactation and is shaped by maternal weight and mode of delivery
2012
Background Breast milk is recognized as the most important postpartum element in metabolic and immunologic programming of health of neonates. The factors influencing the milk microbiome and the potential impact of microbes on infant health have not yet been uncovered. Objective Our objective was to identify pre- and postnatal factors that can potentially influence the bacterial communities inhabiting human milk. Design We characterized the milk microbial community at 3 different time points by pyrosequencing and quantitative polymerase chain reaction in mothers (n = 18) who varied in BMI, weight gain, and mode of delivery. Results We found that the human milk microbiome changes over lactati…
Maternal Metabolic Health Parameters During Pregnancy in Relation to Early Childhood BMI Trajectories
2018
Objective The objective of this study was to evaluate the associations between maternal metabolic parameters and early childhood BMI trajectories. Methods Two thousand two hundred fifty-one children born in Spain between 2004 and 2008 were analyzed. Five BMI z score trajectories from birth to age 4 years were identified by using latent class growth analysis. Multinomial regression assessed the associations between maternal metabolic parameters and offspring's BMI trajectories. Results Children in the reference BMI trajectory had average size at birth followed by a slower BMI gain. Maternal prepregnancy obesity was associated with trajectories of accelerated BMI gain departing from either hi…