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571.
Constantinos K. Zacharis Paraskevas D. Tzanavaras Konstantinos Roubos Kico Dhima 《Journal of chromatography. A》2010,1217(38):5896-5900
In this work, we propose solvent-based de-emulsification dispersive liquid–liquid microextraction (SD-DLLME) as a simple, rapid and efficient sample pretreatment technique for the extraction and preconcentration of organochlorine pesticides (OCPs) from environmental water samples. Separation and analysis of fifteen OCPs was carried out by gas chromatography–mass spectrometry (GC/MS). Parameters affecting the extraction efficiency were systematically investigated. The detection limits were in the range of 2–50 ng L−1 using selective ion monitoring (SIM). The precision of the proposed method, expressed as relative standard deviation, varied between 3.5 and 10.2% (n = 5). Results from the analysis of spiked environmental water samples at the low-ppb level met the acceptance criteria set by the EPA. 相似文献
572.
Gillian R. Hilton Konstantinos Thalassinos Megan Grabenauer Narinder Sanghera Susan E. Slade Thomas Wyttenbach Philip J. Robinson Teresa J. T. Pinheiro Michael T. Bowers James H. Scrivens 《Journal of the American Society for Mass Spectrometry》2010,21(5):845-854
The prion protein (PrP) is implicitly involved in the pathogenesis of transmissible spongiform encephalopathies (TSEs). The
conversion of normal cellular PrP (PrPC), a protein that is predominantly α-helical, to a β-sheet-rich isoform (PrPSc), which has a propensity to aggregate, is the key molecular event in prion diseases. During its short life span, PrP can
experience two different pH environments; a mildly acidic environment, whilst cycling within the cell, and a neutral pH when
it is glycosyl phosphatidylinositol (GPI)-anchored to the cell membrane. Ion mobility (IM) combined with mass spectrometry
has been employed to differentiate between two conformational isoforms of recombinant Syrian hamster prion protein (SHaPrP).
The recombinant proteins studied were α-helical SHaPrP(90-231) and β-sheet-rich SHaPrP(90-231) at pH 5.5 and pH 7.0. The recombinant
proteins have the same nominal mass-to-charge ratio (m/z) but differ in their secondary and tertiary structures. A comparison of traveling-wave (T-Wave) ion mobility and drift cell
ion mobility (DCIM) mass spectrometry estimated and absolute cross-sections showed an excellent agreement between the two
techniques. The use of T-Wave ion mobility as a shape-selective separation technique enabled differentiation between the estimated
cross-sections and arrival time distributions (ATDs) of α-helical SHaPrP(90-231) and β-sheet-rich SHaPrP(90-231) at pH 5.5.
No differences in cross-section or ATD profiles were observed between the protein isoforms at pH 7.0. The findings have potential
implications for a new ante-mortem screening assay, in bodily fluids, for prion misfolding diseases such as TSEs. 相似文献
573.
Leonidas Pitsoulis Konstantinos Papalamprou Balázs Kotnyek 《Discrete Mathematics》2009,309(16):5024-5042
We present a polynomial time algorithm to construct a bidirected graph for any totally unimodular matrix B by finding node-edge incidence matrices Q and S such that QB=S. Seymour’s famous decomposition theorem for regular matroids states that any totally unimodular (TU) matrix can be constructed through a series of composition operations called k-sums starting from network matrices and their transposes and two compact representation matrices B1,B2 of a certain ten element matroid. Given that B1,B2 are binet matrices we examine the k-sums of network and binet matrices. It is shown that thek-sum of a network and a binet matrix is a binet matrix, but binet matrices are not closed under this operation for k=2,3. A new class of matrices is introduced, the so-called tour matrices, which generalise network, binet and totally unimodular matrices. For any such matrix there exists a bidirected graph such that the columns represent a collection of closed tours in the graph. It is shown that tour matrices are closed under k-sums, as well as under pivoting and other elementary operations on their rows and columns. Given the constructive proofs of the above results regarding the k-sum operation and existing recognition algorithms for network and binet matrices, an algorithm is presented which constructs a bidirected graph for any TU matrix. 相似文献
574.
575.
An important problem in logistic regression modeling is the existence of the maximum likelihood estimators. In particular, when the sample size is small, the maximum likelihood estimator of the regression parameters does not exist if the data are completely, or quasicompletely separated. Recognizing that this phenomenon has a serious impact on the fitting of the density ratio model–which is a semiparametric model whose profile empirical log-likelihood has the logistic form because of the equivalence between prospective and retrospective sampling–we suggest a linear programming methodology for examining whether the maximum likelihood estimators of the finite dimensional parameter vector of the model exist. It is shown that the methodology can be effectively utilized in the analysis of case–control gene expression data by identifying cases where the density ratio model cannot be applied. It is demonstrated that naive application of the density ratio model yields erroneous conclusions. 相似文献
576.
Konstantinos Tsioris Waseem K. Raja Eleanor M. Pritchard Bruce Panilaitis David L. Kaplan Fiorenzo G. Omenetto 《Advanced functional materials》2012,22(2):330-335
Microneedles are emerging as a minimally invasive drug delivery alternative to hypodermic needles. Current material systems utilized in microneedles impose constraints hindering the further development of this technology. In particular, it is difficult to preserve sensitive biochemical compounds (such as pharmaceuticals) during processing in a single microneedle system and subsequently achieve their controlled release. A possible solution involves fabricating microneedles systems from the biomaterial silk fibroin. Silk fibroin combines excellent mechanical properties, biocompatibility, biodegradability, benign processing conditions, and the ability to preserve and maintain the activity of biological compounds entrained in its material matrix. The degradation rate of silk fibroin and the diffusion rate of the entrained molecules can be controlled simply by adjusting post‐processing conditions. This combination of properties makes silk an ideal choice to improve on existing issues associated with other microneedle‐based drug delivery system. In this study, a fabrication method to produce silk biopolymer microstructures with the high aspect ratios and mechanical properties required to manufacture microneedle systems is reported. Room temperature and aqueous‐based micromolding allows for the bulk loading of these microneedles with labile drugs. The drug release rate is decreased 5.6‐fold by adjusting the post‐processing conditions of the microneedles, mainly by controlling the silk protein secondary structure. The release kinetics are quantified in an in vitro collagen hydrogel model, which allows tracking of the model drug. Antibiotic loaded silk microneedles are manufactured and used to demonstrate a 10‐fold reduction of bacterial density after their application. The processing strategies developed in this study can be expanded to other silk‐based structural formats for drug delivery and biologicals storage applications. 相似文献
577.
Colodrero RM Olivera-Pastor P Losilla ER Aranda MA Leon-Reina L Papadaki M McKinlay AC Morris RE Demadis KD Cabeza A 《Dalton transactions (Cambridge, England : 2003)》2012,41(14):4045-4051
A new flexible ultramicroporous solid, La(H(5)DTMP)·7H(2)O (1), has been crystallized at room temperature using the tetraphosphonic acid H(8)DTMP, hexamethylenediamine-N,N,N',N'-tetrakis(methylenephosphonic acid). Its crystal structure, solved by synchrotron powder X-ray diffraction, is characterised by a 3D pillared open-framework containing 1D channels filled with water. Upon dehydration, a new related crystalline phase, La(H(5)DTMP) (2) is formed. Partial rehydration of 2 led to La(H(5)DTMP)·2H(2)O (3). These new phases contain highly corrugated layers showing different degrees of conformational flexibility of the long organic chain. The combination of the structural study and the gas adsorption characterization (N(2) and CO(2)) suggests an ultramicroporous flexible framework. NO isotherms are indicative of a strong irreversible adsorption of NO within the pores. Impedance data indicates that 1 is a proton-conductor with a conductivity of 8 × 10(-3) S cm(-1) at 297 K and 98% of relative humidity, and an activation energy of 0.25 eV. 相似文献
578.
Yan Li Ran Li Shujie Pang Bingqing Chen Konstantinos Georgarakis Alain Le Moulec Gavin Vaughan Tao Zhang Alain R. Yavari 《Journal of Non》2012,358(2):150-154
Using viscosity measurement method and in-situ heating synchrotron radiation, the viscosity of the (Zr0.55Al0.1Ni0.05Cu0.3)100 ? xYx (x = 0, 0.5, 1, 2) bulk metallic glasses (BMGs) in their supercooled liquid regions (SLRs) and the in-situ heating nucleation were investigated, respectively. In the SLR, the (Zr0.55Al0.1Ni0.05Cu0.3)99Y1 metallic glass which shows distinct plastic strain in compression exhibits higher viscosity than the other three BMGs, however their Poisson's ratios are almost the same. The synchrotron diffraction results show that crystallization happened in the SLR of the (Zr0.55Al0.1Ni0.05Cu0.3)99Y1 glassy alloy, which could be the reason for the higher viscosity and larger plastic strain in compression compared to the other three alloys. The fracture surfaces of the glassy alloys were observed and analyzed. 相似文献
579.
Aristeidis E. Niotis Christos Mastichiadis Panagiota S. Petrou Ion Christofidis Sotirios E. Kakabakos Athanasia Siafaka-Kapadai Konstantinos Misiakos 《Analytical and bioanalytical chemistry》2010,396(3):1187-1196
The early diagnosis of acute myocardial infarction requires the determination of several markers in serum shortly after its
incidence. The markers most widely employed are the isoenzyme MB of creatine kinase (CK-MB) and the cardiac troponin I (cTnI).
In the present work, a capillary waveguide fluoroimmunosensor for fast and highly sensitive simultaneous determination of
these markers in serum samples is demonstrated. The dual-analyte immunosensor was realized using glass capillaries internally
modified with an ultrathin poly(dimethylsiloxane) film by creating discrete bands of analyte-specific antibodies. The capillary
was then filled with a mixture of sample and biotinylated detection antibodies followed by reaction with streptavidin–horseradish
peroxidase and incubation with a fluorescently labeled tyramide derivative to accumulate fluorescent labels onto immunoreaction
bands. Upon scanning the capillary with a laser beam, part of the emitted fluorescence is trapped and waveguided through the
capillary wall to a photomultiplier placed on one of its ends. The employment of tyramide signal amplification provided detection
limits of 0.2 and 0.5 ng/mL for cTnI and CK-MB, respectively, in a total assay time of 30 min compared to 0.8 and 0.6 ng/mL
obtained for the corresponding assays when the conventional fluorescent label R-phycoerythrin was used in a 65-min assay.
In addition, the proposed immunosensor provided accurate and repeatable measurements (intra-assay and interassay coefficients
of variation lower than 10%), and the values determined in serum samples were in good agreement with those obtained with commercially
available enzyme immunoassays. Thus, the proposed capillary waveguide fluoroimmunosensor has all the required characteristics
for fast and reliable diagnosis of acute myocardial infarction.
相似文献
580.
Konstantinos Kalimeris Otmar Scherzer 《Mathematical Methods in the Applied Sciences》2013,36(16):2254-2264
In this paper, we derive time reversal imaging functionals for two strongly causal acoustic attenuation models, which have been proposed recently. The time reversal techniques are based on recently proposed ideas of Ammari et al. for the thermo‐viscous wave equation. Here and there, an asymptotic analysis provides reconstruction functionals from first order corrections for the attenuating effect. In addition, we present a novel approach for higher order corrections. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献