216,810 research outputs found
Can market frictions really explain the price impact asymmetry of block trades? Evidence from the Saudi stock market
No full textWe empirically examine the price impact of block trades, in the Saudi Stock Market over
the time period of 2005-2008. Using a unique dataset of intraday data consisting of 2.3
million block buys and 1.9 million block sales, we find an asymmetry in the price impact of block purchases and sales. The asymmetry persists even when we account for the bidask bias in block trades, which is contrary to the previous literature. Overall, our findings suggest that in an emerging market where institutional trading is relatively scarce, market microstructure cannot explain the asymmetry n the price impact of large trades
Amphiphilic block copolymers : synthesis, self-assembly and applications
No full textSelf-assembly of amphiphilic block copolymers in aqueous solution is one of the most important nanotechnological methods to prepare nanocarriers for
different applications, such as drug delivery, biosensor, nanoreactor and so on. Synthesis of new types of amphiphilic block copolymers with novel
functionality and detailed characterization of self-assembly, influenced by self-assembly methods and different other parameters (molecular weight,
hydrophilic to hydrophobic ratio), are important. Especially, building up the relationship between the self-assembled nanomorphologies and molecule
constitution are helpful to understand amphiphilic block copolymer self-assemble theroy.
In this thesis, I present to you the influence of different parameters on the self-assembly nanostructures for the poly(dimethylsiloxane)-
block-poly(2-methyl-2-oxazoline) (PDMS-b-PMOXA) amphiphilic block copolymers.3D phase diagram clearly shows in which domain the PDMS-b-PMOXA
self-assemble into polymersome. The polymersome are possible for us to constribute the nano-sized based nanoreactor.
In addition, in order to develop more functional amphiphilic block copolymers and enlarge the potential application areas, another two types of
copolymers, grafted poly(2-methyl-2-oxazoline)-graft(ss)-poly(e-caprolactone) (PMOXA-graft(ss)-PCL) and linear poly(2-ethyl-2-oxazoline)-block-
poly(e-caprolactone)-ss-poly(L-lysine) (PEtOXA-b-PCL-ss-PLL), were designed and synthesized with reduction responsiveness, utilizing different
polymerization techniques, including ring openning polymerization and "graft-to" technology. Due to the amphiphilicity of these two types of
copolymers, nanoparticles are formed by them in aqueous solution. The primary evaluation of these two new type amphiphilic block copolymers
demonstrated that they can be promising candidates as smart nanocarries for the application of drug delivery.
In this dissertation, the result of our research have been comprehensivly compared with other publications and results from different groups.
We have new findingS. We find one new nano-object with 80-100 nm diameter, but without hollow aqueous cavity.
We also realize that basing on poly(2-ethyl-2-oxazoline)-block-poly(e-caprolactone)-ss-poly(L-lysine) (PEtOXA-b-PCL-ss-PLL) copolymer, it is possible
to synthesize more functional copolymer, for example introducing the pH-cleavable linker between PEtOXA and PCL, to mimic more closely the virus delivery
gene into cells
Virtual Symposium on Virtual Mind
No full textWhen certain formal symbol systems (e.g., computer programs) are implemented as dynamic physical symbol
systems (e.g., when they are run on a computer) their activity can be interpreted at higher levels (e.g., binary code can be
interpreted as LISP, LISP code can be interpreted as English, and English can be interpreted as a meaningful conversation).
These higher levels of interpretability are called "virtual" systems. If such a virtual system is interpretable as if it had a mind, is
such a "virtual mind" real? This is the question addressed in this "virtual" symposium, originally conducted electronically among
four cognitive scientists: Donald Perlis, a computer scientist, argues that according to the computationalist thesis, virtual minds are
real and hence Searle's Chinese Room Argument fails, because if Searle memorized and executed a program that could pass the
Turing Test in Chinese he would have a second, virtual, Chinese-understanding mind of which he was unaware (as in multiple
personality). Stevan Harnad, a psychologist, argues that Searle's Argument is valid, virtual minds are just hermeneutic
overinterpretations, and symbols must be grounded in the real world of objects, not just the virtual world of interpretations.
Computer scientist Patrick Hayes argues that Searle's Argument fails, but because Searle does not really implement the program:
A real implementation must not be homuncular but mindless and mechanical, like a computer. Only then can it give rise to a mind
at the virtual level. Philosopher Ned Block suggests that there is no reason a mindful implementation would not be a real one
Congenital heart block associated with Sjögren syndrome: case report
No full textBackground: Congenital heart block is a rare complication of pregnancy associated with Sjögren Syndrome that may result in the death of the foetus or infant, or the need for pacing in the newborn or at a later stage.Case report: The case is presented of a 64-year-old patient with primary Sjögren Syndrome and a history of having given birth to two sons with congenital heart block, both of whom required pacing several years later.Conclusion: The literature relating to this association is discussed including the suggested mechanism, long-term outcome of mothers of children with congenital heart block and preventive treatment strategies
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The A/B alternating block versus the modified block in the middle school
No full texttextGiven that math achievement of eighth grade students has shown almost
no growth in the United States over a ten year period (National Assessment of
Educational Progress, United States Department of Education, 1995), this study
attempted to examine the effect a particular schedule design (A/B Alternating
Block and Modified Block) has on student math achievement as measured by a
standardized test (Texas Assessment of Academic Standards), student attendance
and drop out rate. The study attempted to determine whether middle school
students benefit academically, especially in the area of mathematics, from
instruction that is delivered in a Modified Block schedule format as compared to
instruction that is delivered in the A/B Alternating Block schedule design. Four
middle schools were selected according to comparable characteristics such as
campus demographics (ethnicity break down, socio-economic level, etc) and
schedule design in place. Data was collected on student math scores, attendance
and drop out rates.
Findings of the study indicate that overall and over time student
mathematics achievement was higher in schools where students received
instruction in the A/B Alternating Block scheduling format as compared to the
Modified Blocked schools. A closer observation revealed this was true especially
for White and Hispanic students. In reference to student attendance, the study
showed that overall student attendance was higher for those students enrolled in
schools with an A/B Alternating Block scheduling format as opposed to those
enrolled in Modified Blocked Schools. Thus, recommendations for practice would
include the continued implementation of the A/B Alternating Block schedule
design and the continued monitoring over time of math achievement by whole
group and by ethnic background. Finally, recommendations for further research
were made to conduct additional studies to further identify middle school
practices that will facilitate and provide for increased student achievement.Educational Administratio
Methacrylate-based amphiphilic block copolymers in solution and at surfaces : synthesis, characterization and self-assembly
No full textPart 1. Introduction
General concept of polymer self-assembly, synthesis of amphiphilic block copolymers and their application in biotechnology are briefly presented. Special attention is given to the principles of atom transfer radical polymerization (ATRP) and preparation of solid-supported amphiphilic copolymer membranes. Scope of the thesis and the contribution to the current knowledge in the field are presented.
Part 2. Self-organization behavior of methacrylate-based amphiphilic di- and triblock copolymers
ATRP synthesis of amphiphilic di- and triblock copolymers having different hydrophilic-to-hydrophobic block length ratio is described. The investigation of self-assembly of these AB and ABA block copolymers consisting of poly n-butyl methacrylate (B) and poly 2,2-dimethylaminoethyl methacrylate (A) using combination of DLS, NS-TEM, cryo-EM, and AFM is presented and discussed.
Two populations of self-organized structures in aqueous solution, micelles and compound micelles, were detected for diblock copolymers. Triblock copolymers assembled into vesicular structures of uniform sizes. Furthermore it was found that these vesicles tended to compensate the high curvature by additional organization of the polymer chains outside of the membrane. The chain hydrophilicity of the polymers appeared to have a critical impact on the self-assembly response towards temperature change. The self-reorganization of the polymers at different temperatures and its mechanism are revealed.
Part 3. Solid supported block copolymer membranes through interfacial adsorption of charged block copolymer vesicles
The properties of amphiphilic block copolymer membranes make them promising candidates for the development of new (bio-) sensors based on solid-supported biomimetic structures. Here we investigated the interfacial adsorption of polyelectrolyte vesicles on three different model substrates to find the optimum conditions for the formation of planar membranes. The polymer vesicles were obtained and characterized as described in part 2. We observed reorganization of the amphiphilic copolymer chains from vesicular structures into a 1.5±0.04
nm thick layer on the hydrophobic HOPG surface. However, this film starts disrupting and ‘dewetting’ upon drying. In contrast, adsorption of the vesicles on the negatively charged SiO2 and mica substrates induced vesicle fusion and the formation of planar, supported block copolymer films. This process seems to be controlled by the surface charge density of the substrate and the concentration of the block copolymers in solution. The thickness of the copolymer membrane on mica was comparable to the thickness of phospholipids bilayers.
Part 4. Functionalization of gold and silicon surfaces by copolymer brushes using surface-initiated ATRP
To further develop the solid-supported polymer membranes with improved stability and control over the membrane formation, we applied surface-initiated ATRP to grow step-by-step the poly (n-butyl methacrylate)-co-poly(2-dimethylaminoethyl methacrylate) (PBMA-co-PDMAEMA) brushes from gold and silicon substrates. Two different approaches for the initiator immobilization on surfaces were tested to find optimal conditions for the reaction. The polymer brushes were characterized in situ by contact angle measurements, ellipsometry, and XPS. Detachment of the polymer brushes from both substrates allowed an exact determination of molecular weight and polydispersity indexes given by GPC. 1H NMR confirmed the chemical structure of the detached brushes. We used microcontact printing for the structuring of the surface by copolymer brushes.
Part 5. Grafting and characterization of the amphiphilic triblock copolymer membranes from gold supports
Based on the previous experience with the growth of diblock copolymer chains from surfaces and optimized conditions for initiator immobilization (part 4), we continued the developing of the solid-supported copolymer membranes maximally mimicking the structure of biological membrane. Hence, amphiphilic triblock copolymer brushes composed of hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) blocks and a hydrophobic poly(n-butyl methacrylate) (PBMA) middle part were synthesized using a surface-initiated ATRP. ATR-FTIR, PM-IRRAS, ellipsometry, contact angle measurements and AFM were used for the characterization of PHEMA-co-PBMA-co-PHEMA brushes. Additionally, a detachment of the polymer membranes from the solid support and subsequent GPC analyses allowed us to establish their compositions. Treatment of the amphiphilic brushes with block selective solvents led to reversible changes in the polymer surface topography. The PM-IRRAS analysis revealed an increase of the chain tilt towards the gold surface during its growth. It was suggested that the orientation of the
amphiphilic polymer brushes is influenced mainly by the chain lengths and interchain interactions. The presented results could serve as a good starting point for the fabrication of functional solid-supported membranes for biosensing application.
Part 6. Conclusions and Outlook
In this section the achievements of the research work are discussed. Further improvements and applications are proposed
Block Bootstrap Consistency Under Weak Assumptions
No full textThis paper weakens the size and moment conditions needed for typical block bootstrap methods (i.e. the moving blocks, circular blocks, and stationary bootstraps) to be valid for the sample mean of Near-Epoch-Dependent functions of mixing processes; they are consistent under the weakest conditions that ensure the original process obeys a Central Limit Theorem (those of de Jong, 1997, Econometric Theory).� In doing so, this paper extends de Jong's method of proof, a blocking argument, to hold with random and unequal block lengths.� This paper also proves that bootstrapped partial sums satisfy a Functional CLT under the same conditions.Resampling; Time Series; Near Epoch Dependence; Functional Central Limit Theorem
On convergence of the maximum block improvement method
No full textAbstract. The MBI (maximum block improvement) method is a greedy approach to solving optimization problems where the decision variables can be grouped into a finite number of blocks. Assuming that optimizing over one block of variables while fixing all others is relatively easy, the MBI method updates the block of variables corresponding to the maximally improving block at each iteration, which is arguably a most natural and simple process to tackle block-structured problems with great potentials for engineering applications. In this paper we establish global and local linear convergence results for this method. The global convergence is established under the Lojasiewicz inequality assumption, while the local analysis invokes second-order assumptions. We study in particular the tensor optimization model with spherical constraints. Conditions for linear convergence of the famous power method for computing the maximum eigenvalue of a matrix follow in this framework as a special case. The condition is interpreted in various other forms for the rank-one tensor optimization model under spherical constraints. Numerical experiments are shown to support the convergence property of the MBI method
Solid-supported biomimetic membranes based on amphiphilic block copolymers
No full textPlanar artificial membranes based on amphiphilic block copolymers are of high interest due to their potential applications in catalysis, drug screening, sensing, etc. Such polymeric membranes can successfully mimic biological membranes, providing high robustness and stability, which makes them good candidates to be developed in direction of applications. Even though solid-supported polymer membranes have been already investigated to a certain extent, it is still an emerging area. This thesis presents a new generation of biomimetic solid-supported membranes and hybrid polymer-lipid materials, based on amphiphilic block copolymers: poly(dimethylsiloxane)-block-poly(2-methyl-2-oxazoline) (PDMS-b-PMOXA) and poly(ethylene glycol)-block-poly(γ-methyl-ε-caprolactone)-block-poly[(2-dimethylamino) ethyl methacrylate] (PEG-b-PMCL-b-PDMAEMA). The scope was preparation of stable solid-supported membranes and development of different strategies for insertion/attachment of biomolecules into such membranes. Block copolymers were firstly investigated in respect of behavior at the air-water interface. Deposition of the films on different solid supports (silica wafers, glass and gold slides) was achieved by performing transfers of Langmuir monolayers, which provide formation of defect-free films with good reproducibility. Further, deposited films were functionalized by introduction of membrane proteins and enzymes. To get the insights into morphology and thickness, the obtained systems were analyzed by surface-sensitive techniques, such as atomic force microscopy, ellipsometry, and contact angle measurements. Activity of inserted biomolecules was evaluated by electrical conductance measurements and activity assays. This thesis provides valuable impact in the preparation of membranes in a controllable and reproducible way. Furthermore, it presents different strategies for introduction of biomolecules into such systems, in order to obtain tailored functionality and properties. This work impact fundamental understanding and development of functional membranes. Such artificial membranes and hybrid materials can be further adapted for potential applications
A comprehensive study of the relationship of block scheduling to the teaching of mathematics
No full textPlan BBlock scheduling is a topic selected by this researcher. This researcher investigated the effects of block scheduling in relationship to Mathematics instruction. Block scheduling is a very hotly contested subject for schools at this time and this researcher was concerned about the effects of this type of scheduling on high school Mathematics instruction. Block scheduling was developed in response to criticisms regarding the ineffective use of school time. With block scheduling, students take four classes per day, each lasting 90 minutes. Classes are completed in one semester rather than lasting for an entire year under a traditional schedule. Benefits of block scheduling are that students are able to take more courses throughout high school and have more time available for electives. Less time is wasted on transitioning between classes and administrative duties, allowing this time to be used for instruction. Teachers are able to use innovative instructional strategies as they have a longer time period in which to complete their lessons. Issues with block scheduling include students having to focus their attention for longer periods of time. Some teachers continue to use lecturing as their only instructional tool, and 90 minutes is too long for students to listen to lecture. The pace is also much quicker as the classes are completed in one semester rather than one year. Some students have difficulty processing a large amount of information in such a short period of time. Mathematics is a subject that can be difficult to comprehend. This subject builds upon itself and each step must be understood before students can proceed to the next level. Block scheduling does allow more time during each class period to ensure that comprehension occurs, but the course must move at a faster pace so that all content can be covered. Some students have much difficulty with this pace of instruction. Several recommendations have been developed following the research completed in this study. It is important to have the support of the staff, students, parents, and community prior to block scheduling implementation. Community meetings should be held to explain the new system and the benefits to the students. Teachers and faculty members should be afforded the opportunity to visit other schools with a similar scheduling system. In turn, teachers should be surveyed to determine specific training needs they have in teaching under block scheduling. In order for Mathematics instruction to be effective under block scheduling, staff development and training must be a part of the process. Teachers must be trained in a variety of instructional strategies so that the class time can be best utilized. Special training should be offered to teachers on time and classroom management. Time should also be allotted at staff meetings to review and discuss best practices. Teachers must be afforded the opportunity to share concerns, problems, and successes. Mentoring systems have been found to be effective, especially with new teachers. Peer coaching promotes active learning based on the individual teacher’s needs. Mathematics comprehension must be monitored to determine the success of instruction under the block scheduling system. Benchmarks should be developed to study the student grades over the first five years of implementation to ensure that student grades are not declining with the new system. In the event that block scheduling is not conducive to learning Mathematics, schools must be open to modification of the current system. System flexibility is a must in order for education to be a success. The pace of instruction may need to be modified to ensure that in-depth learning is taking place. Surveys should be completed by parents and students on a regular basis to determine the effectiveness of block schedulin
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