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排序方式: 共有105条查询结果,搜索用时 15 毫秒
21.
In this study the role of acoustic feedback instabilities in the tonal airfoil self-noise phenomenon is investigated. First, direct numerical simulations are conducted of the flow around a NACA-0012 airfoil at Re=1×105 and four angles of attack. At the two lowest angles of attack considered the airfoil self-noise exhibits a clear tonal contribution, whereas at the two higher angles of attack the tonal contribution becomes less significant in comparison to the broadband noise. Classical linear stability analysis of time-averaged boundary layer profiles shows that the tonal noise occurs at a frequency significantly lower than that of the most convectively amplified instability wave. Two-dimensional linear stability analysis of the time-averaged flowfield is then performed, illustrating the presence of an acoustic feedback loop involving the airfoil trailing edge. The feedback loop is found to be unstable only for the cases where tonal self-noise is prominent, and is found to self-select a frequency almost identical to that of the tonal self-noise. The constituent mechanisms of the acoustic feedback loop are considered, which appear to explain why the preferred frequency is lower than that of the most convectively amplified instability wave. 相似文献
22.
ERYTHROPOIETIC PROTOPORPHYRIA: PHOTODYNAMIC TRANSFER OF PROTOPORPHYRIN FROM INTACT ERYTHROCYTES TO OTHER CELLS 总被引:1,自引:0,他引:1
Atle Brun André Western Zvi Malik Sverre Sandberg 《Photochemistry and photobiology》1990,51(5):573-577
Erythrocytes in patients with erythropoietic protoporphyria (EPP) contain large amounts of protoporphyrin and are regarded as the main source of protoporphyrin in this disease. Cells in the skin of EPP patients accumulate protoporphyrin released from the erythrocytes and upon sun exposure endothelial cells are photodamaged. In the present study a light-induced transfer of protoporphyrin directly from EPP erythrocytes to cultured cells is demonstrated. Erythrocytes were layered upon cultured cells and irradiated. The nearness of erythrocyte and cultured cell membranes potentiated the transfer of protoporphyrin between these cells. This transfer was rapid and preceded the release of protoporphyrin to proteins in the medium. Further irradiation of the protoporphyrin-enriched cultured cells, after removal of the erythrocytes, caused severe photodamage to the cells and survival was dependent on both the amount of protoporphyrin transferred and on the light fluence. Clinical observations and the results of this study indicate that light energy may be involved in two steps in the pathophysiology of EPP: (A) light-induced release of protoporphyrin from erythrocytes to endothelial cells and (B) photodynamic damage to protoporphyrin-enriched endothelial cells. 相似文献
23.
Mats Andersson H⇘kan Samuelsson Sebastian Sandberg 《Journal d'Analyse Mathématique》2006,98(1):221-247
We introduce a class of (tuples of commuting) unbounded operators on a Banach space, admitting smooth functional calculi, which contains all operators of Helffer-Sjöstrand type and is closed under the action of smooth proper mappings. Moreover, the class is closed under tensor product of commuting operators. In general, and operator in this class has no resolvent in the usual sense, so the spectrum must be defined in terms of the functional calculus. We also consider invariant subspaces and spectral decompositions. 相似文献
24.
Ramström M Sandberg H 《European journal of mass spectrometry (Chichester, England)》2011,17(5):497-506
Vitamin K-dependent carboxylation of glutamic acid (Glu) residues into γ-carboxyglutamic acid (Gla) is a post-translational modification essential for normal protein activity of, for example, proteins involved in the blood coagulation system. These proteins may contain as many as 12 sites for γ-carboxylation within a protein sequence of 45 amino acid residues. In the biopharmaceutical industry, powerful analytical techniques are required for identification and localization of modified sites. We here present comparatively easy and rapid methods for studies of Gla-containing proteins using recent technology. The performances of two mass spectrometric fragmentation techniques, collision-induced dissociation (CID) and electron transfer dissociation (ETD), were evaluated with respect to γ-carboxylated peptides, applying on-line LC-ion trap MS. ETD MS has so far not been reported for Gla-containing peptides and the applicability of CID for heavily γ-carboxylated proteins has not been evaluated. The anticoagulant protein, protein C, containing nine Gla-sites, was chosen as a model protein. After tryptic digestion, three peptides containing Gla-residues were detected by MS; a 1.2 kDa fragment containing two Gla-residues, a 4.5 kDa peptide containing seven residues and also the 5.6 kDa tryptic peptides containing all nine Gla-residues. Regarding the shortest peptide, both CID and ETD provided extensive peptide sequencing. For the larger peptides, fragmentation by CID resulted in loss of the 44 Da CO(2)-group, while little additional fragmentation of the peptide chain was observed. In contrast, ETD resulted in comprehensive fragmentation of the peptide backbone. The study demonstrates that the combination of both techniques would be beneficial and complementary for investigation of γ-carboxylated proteins and peptides. 相似文献
25.
P. A. Aarnio J. T. Routti J. V. Sandberg 《Journal of Radioanalytical and Nuclear Chemistry》1988,124(2):457-465
The widely used SAMPO Ge(Li) and HPGe gamma spectrum analysis program has been adapted to IBM Personal Computers in a thoroughly revised version MicroSAMPO. The program is intended for peak search, peak fitting, nuclide identification and activity calculations. The use of calibrated peak shape functions for peak area determination makes it possible to resolve complex multiplets with strongly overlapping peaks. Menu-driven user interface, colour graphics diplays, semi-automatic calibrations and interactive options have been designed to make the program more user-friendly. It is well suited for both spectroscopic research and routine analysis. 相似文献
26.
Erythrocytes from patients with erythropoietic protoporphyria (EPP) contain large amounts of protoporphyrin. By fluorescence microscopy it has been found that the erythrocytes show red fluorescence which fades very rapidly. During irradiation of erythrocytes from patients with EPP, a decrease in the fluorescence intensity and a red shift in the fluorescence emission maximum is observed. Since the human eye has a diminishing sensitivity in the red part of the spectrum, the red shift will augment the fluorescence decrease observed in the microscope. The decrease in fluorescence intensity is greater than what would be expected by photobleaching of protoporphyrin alone. We suggest that the rapid fading of fluorocytes observed in a fluorescence microscope can be explained both by photoinduced detachment of protoporphyrin from hemoglobin followed by a redistribution to the erythrocyte membrane and by protoporphyrin photobleaching. 相似文献
27.
Wilson CM Duty T Sandberg M Persson F Shumeiko V Delsing P 《Physical review letters》2010,105(23):233907
We report the observation of photon generation in a microwave cavity with a time-dependent boundary condition. Our system is a microfabricated quarter-wave coplanar waveguide cavity. The electrical length of the cavity is varied by using the tunable inductance of a superconducting quantum interference device. It is measured at a temperature significantly less than the resonance frequency. When the length is modulated at approximately twice the static resonance frequency, spontaneous parametric oscillations of the cavity field are observed. Time-resolved measurements of the dynamical state of the cavity show multiple stable states. The behavior is well described by theory. Our results may be considered a preliminary step towards demonstrating the dynamical Casimir effect. 相似文献
28.
Premvardhan L Sandberg DJ Fey H Birge RR Büchel C van Grondelle R 《The journal of physical chemistry. B》2008,112(37):11838-11853
Fucoxanthin chlorophyll-a/c 2 protein (FCP), the membrane-intrinsic light harvesting complex from the diatom Cyclotella meneghiniana, is characterized by Stark spectroscopy to obtain a quantitative measure of the excited-state dipolar properties of the constituent pigments. The electro-optical properties of the carotenoid fucoxanthin (Fx), the primary light harvester in FCP, were determined from the Stark spectrum measured in a MeTHF glass (77 K) and compared to the results from electronic-structure calculations. On photon absorption by Fx, a 17 D change in the static dipole moment (|Delta mu|exp), and a somewhat larger |Delta mu|exp at the red edge, are measured for the S 0 --> S 2 (1 (1)A g (-)-like -->1 (1)B u *+-like) transition. The large change in dipole moment indicates that Fx undergoes photoinduced charge transfer (CT), and underscores the influence of the S 2 state on the polarity-dependent excited-state dynamics of Fx that has so far been attributed to, and discussed in terms of, the S 0 and the S 1/ICT states. MNDO-PSDCI and SACCI-CISD calculations indicate that the 1 (1)B u (*+)-like state intrinsically possesses a dipole moment much smaller than the 2 (1)A g (*-)-like state, suggesting that solvent fields promote the mixing of these two states and could account for the large dipole moments measured here for the S 0 --> S 2 transition. These CT properties of the 1 (1)B u (*+)-like state of Fx are further enhanced in the protein and underpin its photosynthetic capabilities for light harvesting and energy transfer (ET). In FCP, the CT properties of the Fx's vary according to the energetic position: between 450 and 500 nm there appear to be two sets of Fx's that exhibit |Delta mu| exp values on the order of 5 and 15 D, whereas the red-most Fx's, that are very efficient in ET to chlorophyll-a (Chl-a), exhibit strikingly large |Delta mu| exp values on the order of 40 D. Such magnitudes of |Delta mu| exp suggest a mechanism that enhances Coulombic coupling to promote ET from the S 2 state of Fx to Chl-a. These three sets of Fx's, including a fourth red Fx, are identified by fitting the Stark spectrum of FCP with the Stark spectrum of Fx in MeTHF. In contrast to the Fx's in the protein, the electrostatic properties of the Chl's in FCP are comparatively much smaller. Notably, for the Q y band of Chl-a, a |Delta mu| exp of 0.92 D and a change in polarizability ( Delta alpha exp) of 20 A (3), indicate that the Chl-a's are monomeric in nature and decoupled from each other. 相似文献
29.
Pressurized hot water extraction (PHWE) conditions (time, temperature, pressure) were optimized for the extraction of naringenin and other major flavonoids (dihydrokaempferol, naringin) from knotwood of aspen. Extracts were analysed by GC-FID, GC-MS, HPLC-UV and HPLC-MS. The results were compared with those obtained by Soxhlet, ultrasonic extraction and reflux in methanol. Flavonoids were most efficiently extracted with PHWE at 150 °C and 220 bar with 35 min extraction time. Soxhlet with methanol gave slightly higher recoveries, but an extraction time of 48 h was required. Naringenin concentration was highest in knotwood (1.15% dry weight) and much lower in the sapwood. PHWE proved to be cheap, fast and effective for the isolation of biofunctional flavonoids from aspen knotwood, producing higher recoveries than 24 h Soxhlet extraction, sonication or 24 h reflux. 相似文献
30.
Lars Sandberg 《Journal of computer-aided molecular design》2014,28(3):211-219
An implicit solvent model described by a non-simple dielectric medium is used for the prediction of hydration free energies on the dataset of 47 molecules in the SAMPL4 challenge. The solute is represented by a minimal parameter set model based on a new all atom force-field, named the liquid simulation force-field. The importance of a first solvation shell correction to the hydration free energy prediction is discussed and two different approaches are introduced to address it: either with an empirical correction to a few functional groups (alcohol, ether, ester, amines and aromatic nitrogen), or an ab initio correction based on the formation of a solute/explicit water complex. Both approaches give equally good predictions with an average unsigned error <1 kcal/mol. Chemical accuracy is obtained. 相似文献