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Sökning: WFRF:(Dehlendorff Christian)

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  • Tian, Guoda, et al. (författare)
  • Amplitude and Phase Estimation for Absolute Calibration of Massive MIMO Front-Ends
  • 2020
  • Ingår i: ICC 2020 - 2020 IEEE International Conference on Communications (ICC). - : IEEE - Institute of Electrical and Electronics Engineers Inc.. - 9781728150895
  • Konferensbidrag (refereegranskat)abstract
    • Massive multiple-input multiple-output (MIMO) promises significantly higher performance relative to conventional multiuser systems. However, the promised gains of massive MIMO systems rely heavily on the accuracy of the absolute front-end calibration, as well as quality of channel estimates at the base station (BS). In this paper, we analyze user equipment-aided calibration mechanism to estimate the amplitude scaling and phase drift at each radio-frequency chain interfacing with the BS array. Assuming a uniform linear array at the BS and Ricean fading, we obtain the estimation parameters with moment-based (amplitude, phase) and maximum-likelihood (phase-only) estimation techniques. In stark contrast to previous works, we mathematically articulate the equivalence of the two approaches for phase estimation. Furthermore, we rigorously derive a Cramer-Rao lower bound to characterize the accuracy of the two estimators. Via numerical simulations, we evaluate the estimator performance with varying dominant line-of-sight powers, dominant angles-of-arrival, and signal-to-noise ratios.
  • Dehghani, F., et al. (författare)
  • Inhibition of microglial and astrocytic inflammatory responses by the immunosuppressant mycophenolate mofetil
  • 2010
  • Ingår i: Neuropathology and Applied Neurobiology. - 0305-1846 .- 1365-2990. ; 36:7, s. 598-611
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims: Nucleotide depletion induced by the immunosuppressant mycophenolate mofetil (MMF) has been shown to exert neuroprotective effects. It remains unclear whether nucleotide depletion directly counteracts neuronal demise or whether it inhibits microglial or astrocytic activation, thereby resulting in indirect neuroprotection. Methods: Effects of MMF on isolated microglial cells, astrocyte/microglial cell co-cultures and isolated hippocampal neurones were analysed by immunocytochemistry, quantitative morphometry, and elisa. Results: We found that: (i) MMF suppressed lipopolysaccharide-induced microglial secretion of interleukin-1 beta, tumour necrosis factor-alpha and nitric oxide; (ii) MMF suppressed lipopolysaccharide-induced astrocytic production of tumour necrosis factor-alpha but not of nitric oxide; (iii) MMF strongly inhibited proliferation of both microglial cells and astrocytes; (iv) MMF did not protect isolated hippocampal neurones from excitotoxic injury; and (v) effects of MMF on glial cells were reversed after treatment with guanosine. Conclusions: Nucleotide depletion induced by MMF inhibits microglial and astrocytic activation. Microglial and astrocytic proliferation is suppressed by MMF-induced inhibition of the salvage pathway enzyme inosine monophosphate dehydrogenase. The previously observed neuroprotection after MMF treatment seems to be indirectly mediated, making this compound an interesting immunosuppressant in the treatment of acute central nervous system lesions.
  • Dehghani, H., et al. (författare)
  • The role of microscale solid matrix compressibility on the mechanical behaviour of poroelastic materials
  • 2020
  • Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier. - 0997-7538. ; 83
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the macroscale three-dimensional numerical solution of anisotropic Biot's poroelasticity, with coefficients derived from a micromechanical analysis as prescribed by the asymptotic homogenisation technique. The system of partial differential equations (PDEs) is discretised by finite elements, exploiting a formal analogy with the fully coupled thermal displacement systems of PDEs implemented in the commercial software Abaqus. The robustness of our computational framework is confirmed by comparison with the well-known analytical solution of the one-dimensional Therzaghi's consolidation problem. We then perform three-dimensional numerical simulations of the model in a sphere (representing a biological tissue) by applying a given constant pressure in the cavity. We investigate how the macroscale radial displacements (as well as pressures) profiles are affected by the microscale solid matrix compressibility (MSMC). Our results suggest that the role of the MSMC on the macroscale displacements becomes more and more prominent by increasing the length of the time interval during which the constant pressure is applied. As such, we suggest that parameter estimation based on techniques such as poroelastography (which are commonly used in the context of biological tissues, such as the brain, as well as solid tumours) should allow for a sufficiently long time in order to give a more accurate estimation of the mechanical properties of tissues.
  • Tian, Fei, et al. (författare)
  • Endothelial cells are activated during hypoxia via endoglin/ALK-1/SMAD1/5 signaling in vivo and in vitro
  • 2010
  • Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier Inc. - 0006-291X .- 1090-2104. ; 392:3, s. 283-288
  • Tidskriftsartikel (refereegranskat)abstract
    • Endoglin (ENG) promotes angiogenesis by enhancing activation of TGF-beta type I receptors ALK-1 and ALK-5. ALK-1 phosphorylates transcription factors SMAD1/5, which bind to BMP-responsive elements (BRE), whereas ALK-5 phosphorylates SMAD3, which binds to CAGA elements. Expression of ENG is increased during myocardial infarction (MI). We investigated which ENG signaling pathway is activated in endothelial cells during hypoxia. Expression of ENG, ALK-1, ALK-5, and phosphorylated SMAD1/3/5 by immunostaining and immunoblotting in a mouse model of myocardial infarction (MI) and in hypoxic human aortic endothelial cells (HAECs) was evaluated. Activation of BRE and CAGA was measured by luciferase assays in cells transfected with plasmids expressing ENG or ALK-1 and the number of cells was quantified. mRNA expression of the target genes of TGF-beta signaling, ID1 and BCL-X, was quantified by real-time RT-PCR. Expression of ENG, ALK-1 and phosphorylated SMAD1/5, but not ALK-5 or phosphorylated SMAD3, was significantly increased in hypoxic endothelial cells in vivo and in vitro. Overexpression of both ENG and ALK-1 significantly increased BRE but not CAGA activity, expression of ID1 and BCL-X and the number of HAECs at hypoxia. ENG/ALK-1 signaling is one of the factors that regulate endothelial cell activity during adaptive cardiac angiogenesis.
  • Tian, Fuyang, et al. (författare)
  • Impact of aluminum doping on the thermo-physical properties of refractory medium-entropy alloys
  • 2017
  • Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 121:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the elastic moduli, ideal tensile strength, and thermodynamic properties of TiVNb and AlTiVNb refractory medium-entropy alloys (HEAs) by using ab initio alloy theories: the coherent potential approximation (CPA), the special quasi-random supercell (SQS), and a 432-atom supercell (SC). We find that with increasing number of alloy components, the SQS elastic constants become sensitive to the supercell size. The predicted elastic moduli are consistent with the available experiments. Aluminum doping decreases the stability of the body centered cubic phase. The ideal tensile strength calculation indicates that adding equiatomic Al to TiVNb random solid solution increases the intrinsic strength (ideal strain increase from 9.6% to 11.8%) and decreases the intrinsic strength (from 9.6 to 5.7GPa). Based on the equation of states calculated by the CPA and SC methods, the thermodynamic properties obtained by the two ab initio methods are assessed. The L2(1) AlTiVNb (Ti-Al-V-Nb) alloy is predicted to be thermodynamically and dynamically stable with respect to the solid solution.
  • Tian, Fuyang, et al. (författare)
  • Predicting single phase CrMoWX high entropy alloys from empirical relations in combination with first-principles calculations
  • 2017
  • Ingår i: Intermetallics (Barking). - : Elsevier. - 0966-9795 .- 1879-0216. ; 83, s. 9-16
  • Tidskriftsartikel (refereegranskat)abstract
    • We use the Hume-Rothery rules and ab initio mixing enthalpies to design novel high entropy alloys composed of late 3d metal (Mn, Fe, Co, Ni, Cu) and CrMoW. Results predict that CrMoW, CrMoWMn, CrMoWCo and CrMoWNi adopt single body-centered cubic (bcc) crystal structure. The ab initio calculations of elastic moduli and ideal strengths indicate that the bcc phase is more stable thermodynamically than the face-centered cubic (fcc) crystal structure for CrMoW, CrMoWMn, CrMoWNi HEAs, but the late 3d elements decreases the mechanical stability of the bcc phase. In particular Ni addition increases the intrinsic ductility and decreases the intrinsic strength of CrMoW alloy.
  • Tian, Fei, 1964, et al. (författare)
  • Protein disulfide isomerase increases in myocardial endothelial cells in mice exposed to chronic hypoxia: a stimulatory role in angiogenesis.
  • 2009
  • Ingår i: American Journal of Physiology. Heart and Circulatory Physiology. - 1522-1539 .- 0363-6135. ; 297:3, s. H1078-86
  • Tidskriftsartikel (refereegranskat)abstract
    • Previous studies have shown that exposure to chronic hypoxia protects against myocardial infarction, but little is known about the cellular and molecular mechanisms involved. Here we observed that chronic hypoxia for 3 wk resulted in improved survival of mice (from 64% to 83%), reduced infarction size (from 45 +/- 4% to 32 +/- 4%, P < 0.05), increased cardiac ejection fraction (from 19 +/- 4% to 35 +/- 5%, P < 0.05), coronary flow velocity under adenosine-induced hyperemia (from 58 +/- 2 to 75 +/- 5 cm/s, P < 0.05), myocardial capillary density (from 3,772 +/- 162 to 4,760 +/- 197 capillaries/mm(2), P < 0.01), and arteriolar density (from 8.04 +/- 0.76 to 10.34 +/- 0.69 arterioles/mm(2), P < 0.05) 3 wk after myocardial infarction. With two-dimensional gel electrophoresis, we identified that protein disulfide isomerase (PDI) was highly upregulated in hypoxic myocardial capillary endothelial cells. The loss of PDI function in endothelial cells by small interfering RNA significantly increased the number of apoptotic cells (by 3.4-fold at hypoxia, P < 0.01) and reduced migration (by 52% at hypoxia, P < 0.001) and adhesion to collagen I (by 42% at hypoxia, P < 0.01). In addition, the specific inhibition of PDI by PDI small interfering RNA (by 46%, P < 0.01) and bacitracin (by 72%, P < 0.001) reduced the formation of tubular structures by endothelial cells. Our data indicate that chronic hypoxic exposure improves coronary blood flow and protects the myocardium against infarction. These beneficial effects may be partly explained by the increased endothelial expression of PDI, which protects cells against apoptosis and increases cellular migration, adhesion, and tubular formation. The increased PDI expression in endothelial cells may be a novel mechanism to protect the myocardium against myocardial ischemic diseases.
  • Tian, Feng, et al. (författare)
  • Seasonal co-variation of plant water storage, canopy greenness, and groundwater storage across the globe
  • 2018
  • Konferensbidrag (refereegranskat)abstract
    • Plant water storage is fundamental to the functioning of terrestrial ecosystems by participating in plant metabolism, nutrient and sugar transport, and maintenance of the integrity of the hydraulic system of the plant. However, a global view of the size and dynamics of the water pools stored in plant tissues is still lacking. Here, we report global patterns of seasonal variations in ecosystem-scale plant water storage and their relationship with leaf phenology and groundwater variability, based on space-borne measurements of L-band vegetation optical depth. We find that seasonal variations in plant water storage are highly synchronous with leaf phenology for the boreal and temperate forests, but asynchronous for the tropical woodlands, where the seasonal development of plant water storage lags behind leaf area by up to 180 days. Contrasting patterns of the time lag between plant water storage and terrestrial groundwater storage are also evident in these ecosystems. A comparison of the water cycle components in seasonally dry tropical woodlands highlights the buffering effect of plant water storage on the seasonal dynamics of water supply and demand. Our results offer insights into ecosystem-scale plant water relations globally and provide a basis for an improved parameterization of eco-hydrological and Earth system models.
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