947 research outputs found
The Mod-2 Cohomology Ring of the Third Conway Group is Cohen-Macaulay
By explicit machine computation we obtain the mod-2 cohomology ring of the
third Conway group Co_3. It is Cohen-Macaulay, has dimension 4, and is detected
on the maximal elementary abelian 2-subgroups.Comment: 12 pages; writing style now more concis
Representations and -theory of Discrete Groups
Let be a discrete group of finite virtual cohomological dimension
with certain finiteness conditions of the type satisfied by arithmetic groups.
We define a representation ring for , determined on its elements of
finite order, which is of finite type. Then we determine the contribution of
this ring to the topological -theory , obtaining an exact
formula for the difference in terms of the cohomology of the centralizers of
elements of finite order in .Comment: 4 page
Infinite loop spaces and nilpotent K-theory
Using a construction derived from the descending central series of the free
groups, we produce filtrations by infinite loop spaces of the classical
infinite loop spaces , , , , , and
. We show that these infinite loop spaces are the zero
spaces of non-unital -ring spectra. We introduce the notion of
-nilpotent K-theory of a CW-complex for any , which extends the
notion of commutative K-theory defined by Adem-G\'omez, and show that it is
represented by , were is the -th term of
the aforementioned filtration of .
For the proof we introduce an alternative way of associating an infinite loop
space to a commutative -monoid and give criteria when it can be
identified with the plus construction on the associated limit space.
Furthermore, we introduce the notion of a commutative -rig and show
that they give rise to non-unital -ring spectra.Comment: To appear in Algebraic and geometric topolog
Democratic Social Movement Framing Dynamics: Framing of the Oromo Protest Movement by the International News Media, Oromo Activists, International Human Rights Groups, and the Ethiopian Government Officials
Although there is a plethora of literature on social movements in the fields of sociology and political science, fewer studies exist on the subject in the field of media studies, especially in Africa. While scholarship on the role of social media is emerging in recent years, the literature on the news media coverage of social movements vis-Ă -vis international human rights organizations that also have a role in shaping the discourse is absent. The aim of this project was, therefore, to understand the framing dynamics in the discourse around social movements by the international news media, local activists, international human rights organizations, and government officials. It analyzed the 2015-2016 Oromo protest movement against injustices by the Ethiopian government to examine: (1) the major themes highlighted by these actors, and 2) the framing dynamics between the actorsâ frames. Qualitative framing analysis was used to examine texts of international news media outlets, Facebook messages of prominent Oromo activists, reports and statements of Human Right Watch and Amnesty International, and the Ethiopian government officialsâ response to the protests. The findings reveal that three major themesâcause of the protest, government response to the protest, and call for actionâdominated the texts of the news media, activists, and human rights groups. These themes were framed as various political and economic grievances, violence, and third-party intervention for justice, respectively. The themes and frames of the news media and human rights organizations largely supported the themes and frames highlighted by protest activists. Similar themes were highlighted in the texts of the government officials but were used to counter-frame the frames of other actors (ex: portraying the protesters as violent). The findings have significant implications. They may guide democratic social movement activists in the social media age who want to design similar protests against authoritarian governments in an international arena. The findings bolster existing studies on the use of collective action framing and the relationship between news media and activists. Additionally, the results suggest that international human rights organization are also âsignifying agentsâ engaged in creating meanings and shaping discourse about social movements
Low-rank solutions to the stochastic Helmholtz equation
In this paper, we consider low-rank approximations for the solutions to the
stochastic Helmholtz equation with random coefficients. A Stochastic Galerkin
finite element method is used for the discretization of the Helmholtz problem.
Existence theory for the low-rank approximation is established when the system
matrix is indefinite. The low-rank algorithm does not require the construction
of a large system matrix which results in an advantage in terms of CPU time and
storage. Numerical results show that, when the operations in a low-rank method
are performed efficiently, it is possible to obtain an advantage in terms of
storage and CPU time compared to computations in full rank. We also propose a
general approach to implement a preconditioner using the low-rank format
efficiently
Animal Models in Exosomes Research: What the Future Holds
Exosomes have been implicated in a wide range of pathological and nonpathological processes. Research on tumor-derived exosomes uncovered their role on major processes associated with disease progression. Uncontrolled cellular proliferation resulting in tumor growth, metastatic dissemination and modulation of the immune response, are only a few of the central pathological processes in which tumor-derived exosomes have been implicated. These in vivo studies rely on the administration of purified labeled exosomes from cell culture supernatants into circulation of animals or injections of genetically engineered cells that produce labeled exosomes. However, it is not clear that current available techniques actually translate the in vivo implications of exosomes in several biological processes. The variations seen when using different exosomes cell sources, the total amount of exosomes injected in mice and their route of administration as well as the fact that most studies are performed in immunodeficient animals, shows the difficulty to achieve conclusions which are biologically significant. Genetically engineered mouse models (GEMM) could be a promising approach to address the current technical limitations allowing tracing tumor-derived exosomes in a living organism. These models could enhance greatly our knowledge about exosomes in different fields of research, namely cancer
Effects of machining system parameters and dynamics on quality of high-speed milling
This dissertation outlines research on studying the effects of machining parameters such that cutting speed, feed rate, axial depth of cut, radial depth of cut and helix angle on system dynamic stability and the surface quality of high-speed milling. With the use of structural tool modal parameters, the material cutting force coefficients and the axial depth of cut, the system can avoid the chatter phenomenon of the tool at high cutting speeds. The surface roughness finish in the milling process is determined by the machining parameters and tool structure dynamics. To perform high-speed milling, the chance of tool vibration (chatter phenomenon) which affects the cutting tool, must be minimized or eliminated. In this research, the linear and nonlinear mathematical force models including the effect of the helix angle are presented for an end-milling process. The linear force model includes cutting-edge coefficients. The cutting force coefficients are determined for an end-milling process using two methods, the average force method and the optimization technique method. The second method is developed to identify the cutting force coefficients in the milling process by forming the objective functions using the optimization technique to minimize the error between the experimental and the analytical forces. Moreover, this method produced a good force model that approximates the experimental force results, which compared with the average force method. The stability lobe diagrams are created using the analytical method to determine whether the cut is stable or unstable. In addition, simulations are performed to predict stability of the milling process. By comparing simulated and experimental results, the dynamics and stability of the milling operation can be easily identified before performing any cutting operation. The slot milling experiments show that while the system in the chatter region close to the stability limits and the axial depth of cut increased, the system changes from stable chatter to chaotic chatter. Furthermore, the nature of bifurcation in milling is investigated by performing experiments and simulations. The linear and nonlinear mathematical force models are used for simulating end-milling process. Simulated bifurcation diagrams are generated using both models and compared to experimental results. In addition, the effect of the feed rate on the location of the bifurcation point (start and end of bifurcation) is studied. By comparing simulated and experimental results, the simulation using a nonlinear force model is found more accurate in predicting the dynamics and stability of the milling operation. The applications of Taguchi and response surface methodologies (RSM) are used to minimize the surface roughness in the end milling process. Taguchiâs method for optimum selection of the milling process parameters is applied based on the signal to noise ratio and ANOVA analysis of the surface finish. A second-order model contains quadratic terms that have been created between the cutting parameters and surface roughness using response surface methodology (RSM). Surface roughness of the machined surfaces are measured and used to identify the optimum levels of the milling parameters. Based on Taguchi, ANOVA, and RSM analyses, the end milling process can be optimized to improve surface finish quality and machining productivity
Chest injuries in Tikur Anbessa Hospital, Addis Ababa: A three year experience
A review of 72 patients with chest injuries admitted to Tikur Anbessa Hospital in Ethiopia between February 1996 and February 1999 was undertaken. All but one patient were treated with chest drainage. Approximately 85% of the patients were succesfully treated with chest drains leaving no residual defects. This simple, effective and affordable equipment should be made available in all hospitals. Chest drainage is a life-saving procedure for patients with chest injuries which all doctors should be confident with.Kev words: chest injury, chest drain, associated injuries
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