2,151 research outputs found
Understanding the relevance of national culture in international business research: a quantitative analysis
This review is a comprehensive quantitative analysis of the International Business literature whose focus is on national culture. The analysis relies on a broad range of bibliometric techniques as productivity rankings, citation analysis (individual and cumulative), study of collaborative research patterns, and analysis of the knowledge base. It provides insights on (I) faculty and institutional research productivity and performance; (II) articles, institutions, and scholars’ influence in the contents of the field and its research agenda; and (III) national and international collaborative research trends. The study also explores the body of literature that has exerted the greatest impact on the researched set of selected articles.info:eu-repo/semantics/publishedVersio
Microfluidic smartphone quantitation of <i>Escherichia coli</i> in synthetic urine
In spite of the clinical need, there is a major gap in rapid diagnostics for identification and quantitation of E. coli and other pathogens, also regarded as the biggest bottleneck in the fight against the spread of antimicrobial resistant bacterial strains. This study reports for the first time an optical, smartphone-based microfluidic fluorescence sandwich immunoassay capable of quantifying E. coli in buffer and synthetic urine in less than 25 min without sample preparation nor concentration. A limit of detection (LoD) up to 240 CFU/mL, comensurate with cut-off for UTIs (103-105 CFUs/mL) was achieved. Replicas of full response curves performed with 100-107 CFUs/mL of E. coli K12 in synthetic urine yielded recovery values in the range 80-120%, assay reproducibility below 30% and precision below 20%, therefore similar to high-performance automated immunoassays. The unrivalled LoD was mainly linked to the 'open fluidics' nature of the 10-bore microfluidic strips used that enabled passing a large volume of sample through the microcapillaries coated with capture antibody. The new smartphone based test has the potential of being as a rapid, point-of-care test for rule-in of E. coli infections that are responsible for around 80% of UTIs, helping to stop the over-prescription of antibiotics and the monitoring of patients with other symptomatic communicable diseases caused by E. coli at global scale.</p
How dense can one pack spheres of arbitrary size distribution?
We present the first systematic algorithm to estimate the maximum packing
density of spheres when the grain sizes are drawn from an arbitrary size
distribution. With an Apollonian filling rule, we implement our technique for
disks in 2d and spheres in 3d. As expected, the densest packing is achieved
with power-law size distributions. We also test the method on homogeneous and
on empirical real distributions, and we propose a scheme to obtain
experimentally accessible distributions of grain sizes with low porosity. Our
method should be helpful in the development of ultra-strong ceramics and high
performance concrete.Comment: 5 pages, 5 figure
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Antibody Surface Coverage Drives Matrix Interference in Microfluidic Capillary Immunoassays
The performance of biosensors is often optimised in buffers, which brings inconsistencies during applications with biological samples. Current strategies for minimising sample (matrix) interference are complex to automate and miniaturise, involving e.g. sample dilution or recovery of serum/plasma. This study shows the first systematic study using hundreds of actual microfluidic immunoassay fluoropolymer strips to understand matrix interference in microflow systems. As many interfering factors are assay-specific, we have explored matrix interference for a range of enzymatic immunoassays, including a direct mIgG/anti-mIgG, a sandwich cancer biomarker PSA and a sandwich inflammatory cytokine IL-1β. Serum matrix interference was significantly affected by capillary antibody surface coverage, suggesting for the first time the main cause of serum matrix effect is low-affinity serum components (e.g. auto-antibodies) competing with high-affinity antigen for the immobilised antibody. Additional experiments carried out with different capillary diameters confirmed the importance of antibody surface coverage in managing matrix interference. Building on these findings we propose a novel analytical approach where antibody surface coverage and sample incubation times are key for eliminating and/or minimising serum matrix interference, consisting in bioassay optimization carried out in serum instead of buffer, without compromising the performance of the bioassay nor adding extra cost nor steps. This will help establishing a new route towards faster development of modern point-of-care tests and effective biosensors development
WZW branes and gerbes
We reconsider the role that bundle gerbes play in the formulation of the WZW
model on closed and open surfaces. In particular, we show how an analysis of
bundle gerbes on groups covered by SU(N) permits to determine the spectrum of
symmetric branes in the boundary version of the WZW model with such groups as
the target. We also describe a simple relation between the open string
amplitudes in the WZW models based on simply connected groups and in their
simple-current orbifolds.Comment: latex, 4 figures incorporate
Adipose tissue derived stem cells secretome: soluble factors and their roles in regenerative medicine
Stem cells have been long looked at as possible therapeutic vehicles for different health related problems. Among the different
existing stem cell populations, Adipose derived Stem Cells (ASCs) have been gathering attention in the last 10 years. When compared to
other stem cells populations and sources, ASCs can be easily isolated while providing higher yields upon the processing of adipose tissue.
Similar to other stem cell populations, it was initially thought that the main potential of ASCs for regenerative medicine approaches was
intimately related to their differentiation capability. Although this is true, there has been an increasing body of literature describing the
trophic effects of ASCs on the protection, survival and differentiation of a variety of endogenous cells/tissues. Moreover, they have also
shown to possess an immunomodulatory character. This effect is closely related to the ASCs’ secretome and the soluble factors found
within it. Molecules such as hepatocyte growth factor (HGF), granulocyte and macrophage colony stimulating factors, interleukins (ILs)
6, 7, 8 and 11, tumor necrosis factor-α (TNF-α), vascular endothelial growth factor (VEGF), brain derived neurotrophic factor (BDNF),
nerve growth factor (NGF), adipokines and others have been identified within the ASCs’ secretome. Due to its importance regarding future
applications for the field of regenerative medicine, we aim, in the present review, to make a comprehensive analysis of the literature
relating to the ASCs’ secretome and its relevance to the immune and central nervous system, vascularization and cardiac regeneration.
The concluding section will highlight some of the major challenges that remain before ASCs can be used for future clinical applications
Angiogenic potential of gellan gum-based hydrogels for application in nucleus pulposus regeneration : in vivo study
Hydrogels for nucleus pulposus (NP) regeneration should be able to comprise a nonangiogenic or even antiangiogenic
feature. Gellan gum (GG)–based hydrogels have been reported to possess adequate properties for being
used as NP substitutes in acellular and cellular strategies, due to its ability to support cell encapsulation, adequate
mechanical properties, and noncytotoxicity. In this study, the angiogenic response of GG-based hydrogels was
investigated by performing the chorioallantoic membrane assay. The convergence of macroscopic blood vessels
toward the GG, ionic-crosslinked methacrylated GG (iGG-MA), and photo-crosslinked methacrylated GG (phGGMA)
hydrogel discs was quantified. Gelatin sponge (GSp) and filter paper (FP) alone and with vascular endothelial
growth factor were used as controls of angiogenesis. The images obtained were digitally processed and analyzed
by three independent observers. The macroscopic blood vessel quantification demonstrated that the GG-based
hydrogels are not angiogenic as compared with FP controls. No statistical differences between the GG-based
hydrogels tested in respect to its angiogenic ability were observed. Hematoxylin and eosin staining and SNA-lectin
immunohistochemistry assay indicated that the iGG-MA and phGG-MA hydrogels do not allow the ingrowth of
chick endothelial cells, following 4 days of implantation. On the contrary, GG, GSp, and FP controls allowed cell
infiltration. The histological data also indicated that the GG-based hydrogels do not elicit any acute inflammatory
response. The results showed that the GG, iGG-MA, and phGG-MA hydrogels present different permeability to
cells but functioned as a physical barrier for vascular invasion. These hydrogels present promising and tunable
properties for being used as NP substitutes in the treatment of degenerative intervertebral disc.The authors thank the funds provided by Portuguese Foundation for Science and Technology (FCT) through POCTI and FEDER programs (SFRH/BI/33503/2008). This work was also carried out with the support of the European Union funded Collaborative Project Disc Regeneration (NMP3-LA-2008-213904)
Structural and longitudinal analysis of the knowledge base on spin-off research
Following the dynamism in spin-off research, in this study we conduct a structural and longitudinal bibliometric analysis of a sample of 812 articles on spin-offs published in 234 journals included in the ISI Web of Knowledge over a period of three decades. The analyses do not seek to establish a new conceptualization but rather to reveal the intellectual structure of the field and how it has evolved, and the profile of the knowledge network established in the three perspectives: corporate, academic and entrepreneurial spin-offs. The diversity involved in the three streams of spin-off research signals substantial differences. Theoretically, transaction costs, agency and the resource-based view have remained a foundation of spin-off research, albeit that research has been driven more by the phenomena than by developing the theory. The more traditional focus on corporate spin-offs was followed by emphasis on academic spin-offs and more recently on entrepreneurial spin-offs. This shift has been accompanied by a more business/management theoretical orientation, replacing a more financial and taxation-based perspective underlying corporate spin-offs. This study systematizes the existing stock of knowledge and raises avenues for additional inquiry.info:eu-repo/semantics/publishedVersio
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A Lab-in-a-briefcase for rapid prostate specific antigen (PSA) screening from whole blood
We present a new concept for rapid and fully portable Prostate Specific Antigen (PSA) measurement, termed “Lab-in-a-Briefcase”, which integrates an affordable microfluidic ELISA platform utilising a melt-extruded fluoropolymer Micro Capillary Film (MCF) containing 10 bore, 200 μm internal diameter capillaries, a disposable multi-syringe aspirator (MSA) plus a sample tray pre-loaded with all required immunoassay reagents, and a portable film scanner for colorimetric signal digital quantitation. Each MSA can perform 10 replicate microfluidic immunoassays on 8 samples, allowing 80measurements to be made in less than 15 minutes based on semi-automated operation and norequirement of additional fluid handling equipment. An assay was optimised for measurement of a clinically relevant range of PSA from 0.9 to 60.0 ng/ml in 15 minutes with CVs in the order of 5% based on intra-assay variability when read using a consumer flatbed film scanner. The PSA assay performance in the MSA remained robust in the presence of undiluted or 1:2 diluted human serum or whole blood, and the matrix effect could simply be overcome by extending sample incubation times. The PSA "Lab-in-a-briefcase" is particularly suited to a low-resource health setting where diagnostic labs and automated immunoassay systems are not accessible, by allowing PSA measurement outside the laboratory using affordable equipment
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