| 44161. |
- Korner, Anna, et al.
(författare)
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Influence of Different Polymer Types on the Overall Release Mechanism in Hydrophilic Matrix Tablets
- 2009
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Ingår i: Molecules. - : MDPI AG. - 1420-3049. ; 14:8, s. 2699-2716
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Tidskriftsartikel (refereegranskat)abstract
- The effect of three different types of polymer chain structures on the polymer release from hydrophilic matrix tablets was investigated by comparing a synthetic semi-crystalline linear polymer (PEO), a branched amorphous polysaccharide (dextran) and an amorphous substituted cellulose derivative (HPMC). The polymer release rates for tablets containing mixtures of high and low molecular weight grades in different ratios were determined by using a modified USP II method and a SEC-RI chromatography system. The results showed that independent of polymer type: (i) plots of the release versus time had similar shapes, (ii) the release of long and short polymer chains was equal and no fractionation occurred during the release and (iii) the release rate could be related to the average intrinsic viscosity of the polymer mixtures. This confirms the hypothesis that the release rate can be related to a constant viscosity on the surface of the hydrophilic matrix tablet and that it is valid for all the investigated polymers.
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| 44162. |
- Kornev, V. K., et al.
(författare)
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Dynamics of underdamped Josephson junctions with non-sinusoidal current-phase relation
- 2006
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 435:1-2, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- Results on analytical and computational investigations of high-frequency dynamics of Josephson junctions, characterized by non-zero capacitance and the second harmonic in the current-phase relation are presented. These attributes each have influence on the behaviour of integer Shapiro steps and lead to the formation of non-integer Shapiro steps. Analytic theory of the integer and non-integer Shapiro steps has been developed for the so-called high-frequency limit. The analytical and numerical results are compared with experimental data for hybrid heterostructures YBCO/Au/Nb. Detector response for the case of high fluctuation level has been considered as well.
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| 44163. |
- Korniyenko, Yevgeniy, 1989, et al.
(författare)
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Nonlinear response of a ballistic graphene transistor with an ac-driven gate: High harmonic generation and terahertz detection
- 2016
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 94:12
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Tidskriftsartikel (refereegranskat)abstract
- We present results for time-dependent electron transport in a ballistic graphene field-effect transistor with an ac-driven gate. Nonlinear response to the ac drive is derived utilizing Floquet theory for scattering states in combination with Landauer-Buttiker theory for transport. We identify two regimes that can be useful for applications: (i) low and (ii) high doping of graphene under source and drain contacts, relative to the doping level in the graphene channel, which in an experiment can be varied by a back gate. In both regimes, inelastic scattering induced by the ac drive can excite quasibound states in the channel that leads to resonance promotion of higher-order sidebands. Already for weak to intermediate ac drive strength, this leads to a substantial change in the direct current between source and drain. For strong ac drive with frequency Omega, we compute the higher harmonics of frequencies n Omega (n integer) in the source-drain conductance. In regime (ii), we show that particular harmonics (for instance, n = 6) can be selectively enhanced by tuning the doping level in the channel or by tuning the drive strength. We propose that the device operated in the weak-drive regime can be used to detect THz radiation, while in the strong-drive regime, it can be used as a frequency multiplier.
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| 44164. |
- Korniyenko, Yevgeniy, 1989
(författare)
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Quantum theory of time-dependent transport in graphene
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-quality ballistic electronic devices made from graphene are becoming an experimental reality. Carbon-based electronics is heralded if not to succeed or surpass then to complement the existing semiconducting technology. This thesis investigates graphene-based devices from a theoretical point of view with the focus on high-frequency applications, where the material is expected to have a large impact. We develop a quantum-mechanical description of time-dependent transport in mesoscopic graphene samples based on a scattering matrix approach similar to Landauer-Büttiker treatment of non-relativistic charge carriers. We investigate scattering processes involved in transport through a GFET and identify resonant mechanisms that lead to enhancement of the source-drain current under an oscillating gate signal. We propose a tunable selective frequency multiplication scheme and a radiation detector with operation relying on such mechanisms. The performance of the proposed devices is investigated in terms of their shot noise and Fano factor, which we show to be suppressed due to Klein tunnelling even for strong driving of the system. Finally, we apply the formalism to a quantum pump based on an asymmetric potential profile with respect to the gate electrode doping and compute the current through it, revealing that the temperature and the back gate bias can be used to switch the direction of the current.
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| 44165. |
- Korniyenko, Yevgeniy, 1989, et al.
(författare)
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Resonant second-harmonic generation in a ballistic graphene transistor with an ac-driven gate
- 2016
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 93:3
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Tidskriftsartikel (refereegranskat)abstract
- We report a theoretical study of time-dependent transport in a ballistic graphene field effect transistor. We develop a model based on Floquet theory describing Dirac electron transmission through a harmonically driven potential barrier. Photon-assisted tunneling results in excitation of quasibound states at the barrier. Under resonance conditions, the excitation of the quasibound states leads to promotion of higher-order sidebands and, in particular, an enhanced second harmonic of the source-drain conductance. The resonances in the main transmission channel are of the Fano form, while they are of the Breit-Wigner form for sidebands. For weak ac drive strength Z(1), the dynamic Stark shift scales as Z(1)(4), while the resonance broadens as Z(1)(2). We discuss the possibility of utilizing the resonances in prospective ballistic high-frequency devices, in particular frequency doublers operating at high frequencies and low temperatures.
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| 44166. |
- Korniyenko, Yevgeniy, 1989, et al.
(författare)
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Shot noise in a harmonically driven ballistic graphene transistor
- 2017
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 95:16
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Tidskriftsartikel (refereegranskat)abstract
- We study time-dependent electron transport and quantum noise in a ballistic graphene field effect transistor driven by an ac gate potential. The nonlinear response to the ac signal is computed through Floquet theory for scattering states and Landauer-Büttiker theory for charge current and its fluctuations. Photon-assisted excitation of a quasibound state in the top-gate barrier leads to resonances in transmission that strongly influence the noise properties. For strong doping of graphene under source and drain contacts, when electrons are transmitted through the channel via evanescent waves, the resonance leads to a substantial suppression of noise. The Fano factor is then reduced well below the pseudodiffusive value, F<1/3, also for strong ac drive. The good signal-to-noise ratio (small Fano factor) on resonance suggests that the device is a good candidate for high-frequency (THz) radiation detection. We show analytically that Klein tunneling (total suppression of back-reflection) persists for perpendicular incidence also when the barrier is driven harmonically. Although the transmission is inelastic and distributed among sideband energies, a sum rule leads to total suppression of shot noise.
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| 44167. |
- Korosov, Anton Andreevich, et al.
(författare)
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A new tracking algorithm for sea ice age distribution estimation
- 2018
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Ingår i: Cryosphere. - : Copernicus GmbH. - 1994-0424 .- 1994-0416. ; 12:6, s. 2073-2085
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Tidskriftsartikel (refereegranskat)abstract
- A new algorithm for estimating sea ice age (SIA) distribution based on the Eulerian advection scheme is presented. The advection scheme accounts for the observed divergence or convergence and freezing or melting of sea ice and predicts consequent generation or loss of new ice. The algorithm uses daily gridded sea ice drift and sea ice concentration products from the Ocean and Sea Ice Satellite Application Facility. The major advantage of the new algorithm is the ability to generate individual ice age fractions in each pixel of the output product or, in other words, to provide a frequency distribution of the ice age allowing to apply mean, median, weighted average or other statistical measures. Comparison with the National Snow and Ice Data Center SIA product revealed several improvements of the new SIA maps and time series. First, the application of the Eulerian scheme provides smooth distribution of the ice age parameters and prevents product undersampling which may occur when a Lagrangian tracking approach is used. Second, utilization of the new sea ice drift product void of artifacts from EUMETSAT OSI SAF resulted in more accurate and reliable spatial distribution of ice age fractions. Third, constraining SIA computations by the observed sea ice concentration expectedly led to considerable reduction of multi-year ice (MYI) fractions. MYI concentration is computed as a sum of all MYI fractions and compares well to the MYI products based on passive and active microwave and SAR products.
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| 44168. |
- Korotkova, Marina, 1954, et al.
(författare)
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Gender-related long-term effects in adult rats by perinatal dietary ratio of n-6/n-3 fatty acids.
- 2005
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Ingår i: American journal of physiology. Regulatory, integrative and comparative physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 288:3
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Tidskriftsartikel (refereegranskat)abstract
- Epidemiological studies in humans have shown that perinatal nutrition affects health later in life. We have previously shown that the ratio of n-6 to n-3 polyunsaturated fatty acids (PUFA) in the maternal diet affects serum leptin levels and growth of the suckling pups. The aim of the present study was to investigate the long-term effects of various ratios of the dietary n-6 and n-3 PUFA during the perinatal period on serum leptin, insulin, and triacylglycerol, as well as body growth in the adult offspring. During late gestation and throughout lactation, rats were fed an isocaloric diet containing 7 wt% fat, either as linseed oil (n-3 diet), soybean oil (n-6/n-3 diet), or sunflower oil (n-6 diet). At 3 wk of age, the n-6/n-3 PUFA ratios in the serum phospholipids of the offspring were 2.5, 8.3, and 17.5, respectively. After weaning, all pups were given a standard chow. At the 28th postnatal wk, mean body weight and fasting insulin levels were significantly increased in the rats fed the n-6/n-3 diet perinatally compared with the other groups. The systolic blood pressure and serum triacylglycerol levels were only increased in adult male rats of the same group. These data suggest that the balance between n-6 and n-3 PUFA during perinatal development affects several metabolic parameters in adulthood, especially in the male animals.
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| 44169. |
- Korotkova, Marina, 1954, et al.
(författare)
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Leptin levels in rat offspring are modified by the ratio of linoleic to alpha-linolenic acid in the maternal diet
- 2002
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Ingår i: J Lipid Res. ; 43:10, s. 1743-9
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Tidskriftsartikel (refereegranskat)abstract
- The supply of polyunsaturated fatty acids (PUFA) is important for optimal fetal and postnatal development. We have previously shown that leptin levels in suckling rats are reduced by maternal PUFA deficiency. In the present study, we evaluated the effect of maternal dietary intake of (n-3) and (n-6) PUFA on the leptin content in rat milk and serum leptin levels in suckling pups. For the last 10 days of gestation and throughout lactation, the rats were fed an isocaloric diet containing 7% linseed oil (n-3 diet), sunflower oil (n-6 diet), or soybean oil (n-6/n-3 diet). Body weight, body length, inguinal fat pad weight, and adipocyte size of the pups receiving the n-3 diet were significantly lower during the whole suckling period compared with n-6/n-3 fed pups. Body and fat pad weights of the n-6 fed pups were in between the other two groups at week one, but not different from the n-6/n-3 group at week 3. Feeding dams the n-3 diet resulted in decreased serum leptin levels in the suckling pups compared with pups in the n-6/n-3 group. The mean serum leptin levels of the n-6 pups were between the other two groups but not different from either group. There were no differences in the milk leptin content between the groups. These results show that the balance between the n-6 and n-3 PUFA in the maternal diet rather than amount of n-6 or n-3 PUFA per se could be important for adipose tissue growth and for maintaining adequate serum leptin levels in the offspring.
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| 44170. |
- Korotkova, Marina, 1954, et al.
(författare)
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Maternal dietary intake of essential fatty acids affects adipose tissue growth and leptin mRNA expression in suckling rat pups
- 2002
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Ingår i: Pediatric Research. - : Springer Science and Business Media LLC. - 0031-3998 .- 1530-0447. ; 52:1, s. 78-84
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Tidskriftsartikel (refereegranskat)abstract
- We have previously shown that maternal intake of essential fatty acids during late gestation and lactation affects the level of serum leptin in pups. The aim of the present study was to investigate the effect of dietary essential fatty acids on leptin content in the milk of rat dams and leptin expression in white adipose tissue of pups during the suckling period. During late gestation and throughout lactation, rats were fed a control or an essential fatty acid-deficient (EFAD) diet. Milk of the EFAD dams contained more saturated and less polyunsaturated fatty acids compared with the control dams. Milk leptin levels were higher in the EFAD dams than in the control dams at 3 wk of lactation. The weight of inguinal white adipose tissue depots and the serum leptin levels of the EFAD pups were significantly lower than in the control pups during the whole suckling period. In addition, semiquantitative reverse transcriptase-PCR analysis of leptin mRNA levels in inguinal white adipose tissue showed a reduction in the EFAD pups compared with the control pups at 3 wk of age. We conclude that maternal dietary essential fatty acid intake affects serum leptin levels in pups by regulating both the amount of adipose tissue and the leptin mRNA expression.
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