13,359 research outputs found
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Coronavirus mRNA synthesis: identification of novel transcription initiation signals which are differentially regulated by different leader sequences.
The mRNA synthesis of mouse hepatitis virus (MHV) has been proposed to be the result of interaction between the leader RNA and the intergenic sites. Previously, we have identified a transcription initiation site (for mRNA 2-1), which is more efficiently transcribed by viruses containing two copies of UCUAA sequence in the leader RNA than by those with three copies. In this study, we have identified several sites which are regulated in the opposite way, namely, they are efficiently transcribed by the leader RNA with three UCUAA copies but not by those with two copies. These sites were characterized by primer extension and amplification by polymerase chain reaction. One of these sites is in the gene 3 region of a recombinant virus between A59 and JHM strains of MHV. Another is in the gene 2 region of MHV-1 strain. Both of these sites have a sequence similar to but different from the consensus transcription initiation signal (UCUAAUCUAUC and UUUAAUCUU, as opposed to UCUAAAC). These two novel intergenic sequences are not present in the genome of the JHM strain, consistent with the absence of these mRNAs in the JHM-infected cells. The discovery of this type of transcription initiation site provides additional evidence for the importance of the leader RNA in the transcription initiation of MHV mRNAs
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Biosynthesis, structure, and biological activities of envelope protein gp65 of murine coronavirus.
We have previously shown that gp65 (E3) is a virion structural protein which varies widely in quantity among different strains of mouse hepatitis virus (MHV). In this study, the biosynthetic pathway and possible biological activities of this protein were examined. The glycosylation of gp65 in virus-infected cells was inhibited by tunicamycin but not by monensin, suggesting that it contains an N-glycosidic linkage. Glycosylation is cotranslational and appears to be complete before the glycoprotein reaches the Golgi complex. Pulse-chase experiments showed that this protein decreased in size after 30 min of chase, suggesting that the carbohydrate chains of gp65 undergo trimming during its transport across the Golgi. This interpretation is supported by the endoglycosidase treatment of gp65, which showed that the peptide backbone of gp65 did not decrease in size after pulse-chase periods. This maturation pathway is distinct from that of the E1 or E2 glycoproteins. Partial endoglycosidase treatment indicated that gp65 contains 9 to 10 carbohydrate side chains; thus, almost all of the potential glycosylation sites of gp65 were glycosylated. In vitro translation studies coupled with protease digestion suggest that gp65 is an integral membrane protein. The presence of gp65 in the virion is correlated with the presence of an acetylesterase activity. No hemagglutinin activity was detected
An Exploratory Study of Hong Kong Chinese Studentsā Conceptions and Experiences of Academicsā Care within a Higher Education Context
This research investigated Hong Kong Chinese undergraduate studentsā conceptions and experiences of academicsā care and examined its pedagogical implications within a higher education context. Three purposes framed this study: 1) To explore the conceptions of academicsā care amongst Hong Kong Chinese undergraduate students; 2) To investigate Hong Kong Chinese undergraduate studentsā perceived attributes of academicsā care and the perceived effects of academicsā care on learning and development in Hong Kong; and 3) To draw the implications of caring pedagogy for Hong Kong Chinese undergraduate studentsā learning and academic development in Hong Kong.
The empirical data were collected from final-year students in the naturalistic setting of a Hong Kong university. By applying a qualitative research design, purposive sampling was used to select students who had experienced academicsā care during their university study. Data sources included in-depth interviews, write-up accounts and researcherās notes. Thematic analysis was used to identify the themes emerged from the informantsā narrative accounts of academicsā care. Data quality procedures, included triangulation, member checks and audit trail, were followed to ensure research rigour.
Results indicated that academicsā care was conceptualized as a continuum of care, moving along the continuum from āPedagogical Careā to āHolistic Careā and then to āSustainable Careā. This continuum featured a deepening of mutuality, responsiveness and reciprocity. A dual overarching theme of āSafety Netā and āSustainable Bondingā were identified in conceptualizing academicsā care in a university context. This thesis thus proposed a model of caring in higher education rested on three overlapping domains of the relational zone, attachment behaviour and the socio-cultural context.
This thesis has contributed to an under-researched area of caring pedagogy in a university context. The significant role of academicsā care in studentsā learning, development and well-being has been discerned as a key construct of the socio-culture of care within the Chinese context. Implications were thus offered for future research on caring pedagogy, and for policymakers, university administrators and teachers in further exploring the opportunities presented by integrating care into teaching practices
Self-normalized processes: exponential inequalities, moment bounds and iterated logarithm laws
Self-normalized processes arise naturally in statistical applications.
Being unit free, they are not affected by scale changes. Moreover,
self-normalization often eliminates or weakens moment assumptions. In this
paper we present several exponential and moment inequalities, particularly
those related to laws of the iterated logarithm, for self-normalized random
variables including martingales. Tail probability bounds are also derived. For
random variables B_t>0 and A_t, let Y_t(\lambda)=\exp{\lambda A_t-\lambda
^2B_t^2/2}. We develop inequalities for the moments of A_t/B_{t} or sup_{t\geq
0}A_t/{B_t(\log \log B_{t})^{1/2}} and variants thereof, when EY_t(\lambda
)\leq 1 or when Y_t(\lambda) is a supermartingale, for all \lambda belonging to
some interval. Our results are valid for a wide class of random processes
including continuous martingales with A_t=M_t and B_t=\sqrt _t, and sums of
conditionally symmetric variables d_i with A_t=\sum_{i=1}^td_i and
B_t=\sqrt\sum_{i=1}^td_i^2. A sharp maximal inequality for conditionally
symmetric random variables and for continuous local martingales with values in
R^m, m\ge 1, is also established. Another development in this paper is a
bounded law of the iterated logarithm for general adapted sequences that are
centered at certain truncated conditional expectations and self-normalized by
the square root of the sum of squares. The key ingredient in this development
is a new exponential supermartingale involving \sum_{i=1}^td_i and
\sum_{i=1}^td_i^2.Comment: Published by the Institute of Mathematical Statistics
(http://www.imstat.org) in the Annals of Probability
(http://www.imstat.org/aop/) at http://dx.doi.org/10.1214/00911790400000039
Photo-induced reduction of graphene oxide coating on optical waveguide and consequent optical intermodulation
Increased absorption of transverse-magnetic (TM) - polarised light by a graphene-oxide (GO) coated polymer waveguide has been observed in the presence of transverse-electric (TE) - polarised light. The GO-coated waveguide exhibits very strong photo-absorption of TE-polarised light - and acts as a TM-pass waveguide polariser. The absorbed TE-polarised light causes a significant temperature increase in the GO film and induces thermal reduction of the GO, resulting in an increase in optical-frequency conductivity and consequently increased optical propagation loss. This behaviour in a GO-coated waveguide gives the action of an inverted optical switch/modulator. By varying the incident TE-polarised light power, a maximum modulation efficiency of 72% was measured, with application of an incident optical power level of 57āmW. The GO-coated waveguide was able to respond clearly to modulated TE-polarised light with a pulse duration of as little as 100āĪ¼s. In addition, no wavelength dependence was observed in the response of either the modulation (TE-polarised light) or the signal (TM-polarised light)
Switching transients in electrical installations of buildings in Hong Kong
More and more sensitive electronic and computer-based devices or systems are connected to the electrical installations of buildings. Measures to ensure high power quality in the electricity supply network for the satisfactory operation of such equipment is a hot topic of research in electrical engineering. Electrical transients are one of the important issues in power quality. This paper presents the approach and ideas of a project at the University of Hong Kong which addresses this problem with particular emphasis on switching transients in typical electrical installations in Hong Kong buildings.published_or_final_versio
Phase diagram of solution of oppositely charged polyelectrolytes
We study a solution of long polyanions (PA) with shorter polycations (PC) and
focus on the role of Coulomb interaction. A good example is solutions of DNA
and PC which are widely studied for gene therapy. In the solution, each PA
attracts many PCs to form a complex. When the ratio of total charges of PA and
PC in the solution, , equals to 1, complexes are neutral and they condense
in a macroscopic drop. When is far away from 1, complexes are strongly
charged. The Coulomb repulsion is large and free complexes are stable. As
approaches to 1, PCs attached to PA disproportionate themselves in two
competing ways. One way is inter-complex disproportionation, in which PCs make
some complexes neutral and therefore condensed in a macroscopic drop while
other complexes become even stronger charged and stay free. The other way is
intra-complex disproportionation, in which PCs make one end of a complex
neutral and condensed in a small droplet while the rest of the complex forms a
strongly charged tail. Thus each complex becomes a "tadpole". These two ways
can also combine together to give even lower free energy. We get a phase
diagram of PA-PC solution in a plane of and inverse screening radius of the
monovalent salt, which includes phases or phase coexistence with both kinds of
disproportionation.Comment: 29 pages, 10 figures. Major change in results and tex
In Vitro Response of Retinal Pigment Epithelial Cells Exposed to Chitosan Materials Prepared with Different Cross-Linkers
The interaction between cells and biopolymers is the evaluation indicator of the biocompatibility of materials. The purpose of this work was to examine the responses of retinal pigment epithelial (RPE) cells to genipin (GP) or glutaraldehyde (GTA) cross-linked chitosan by means of cell viability assays, cytokine expression analyses, and apoptosis assays. Evaluations of non-cross-linked chitosan were conducted simultaneously for comparison. Both GP and GTA treated samples with the same extent of cross-linking (around 80%) were prepared by varying cross-linking time. Our results showed that GP cross-linking was carried out by either radical polymerization of the monomers or SN2 nucleophilic substitution reaction involving the replacement of the ester group on the monomer with a secondary amide linkage. On the other hand, GTA could react with free amino groups of chitosan, leading to the formation of either the Schiff bases or the Michael-type adducts with terminal aldehydes. The biocompatibility of non-cross-linked chitosan membranes was demonstrated by the absence of any signs of toxicity or inflammation reaction. The present study showed that the ARPE-19 cells exposed to GTA cross-linked chitosan membranes had significantly higher cytotoxicity, interleukin-6 levels, and number of TUNEL-positive nuclei than did those exposed to GP treated samples. In addition, the materials modified with GTA trigger apoptosis at an early stage and may induce toxicity in the RPE cells later. The findings suggest that while the chitosan molecules bridged by GP are satisfactorily cytocompatible, the counterparts treated by GTA do not seem to be tolerated. In terms of material safety, the GP cross-linked chitosan may be compatible with human RPE cells and may have a potential application as delivery carriers in the treatment of posterior segment diseases
Half-dose verteporfin photodynamic therapy for bullous variant of central serous chorioretinopathy: a case report
<p>Abstract</p> <p>Introduction</p> <p>Central serous chorioretinopathy is characterized by serous neurosensory detachment of the macula and it usually resolves spontaneously with good visual prognosis. In some patients, however, the serous retinal detachment might be very extensive and can result in bullous exudative retinal detachment. We evaluated the use of half-dose verteporfin photodynamic therapy for the treatment of bullous retinal detachment in idiopathic central serous chorioretinopathy.</p> <p>Case presentation</p> <p>We report the case of a 51-year-old Chinese man who presented with blurred vision in his right eye and superior visual field defect due to bullous variant of central serous chorioretinopathy. No improvement in vision and retinal detachment was noted after three months of observation and a short course of oral acetazolamide. He was then treated with half-dose verteporfin photodynamic therapy and his visual acuity improved from 20/70 to 20/25 within one month of treatment. Three months after photodynamic therapy, there was complete resolution of sub-retinal fluid and bullous retinal detachment. No recurrence of central serous chorioretinopathy was noted in three years of follow-up.</p> <p>Conclusion</p> <p>We report the beneficial effect of photodynamic therapy with half-dose verteporfin as a treatment option for bullous retinal detachment caused by central serous chorioretinopathy.</p
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