4,682 research outputs found
Finite index subgroups without unique product in graphical small cancellation groups
We construct torsion-free hyperbolic groups without unique product whose
subgroups up to some given finite index are themselves non-unique product
groups. This is achieved by generalising a construction of Comerford to
graphical small cancellation presentations, showing that for every subgroup
of a graphical small cancellation group there exists a free group such that
admits a graphical small cancellation presentation.Comment: 8 pages, 1 figur
Does Housing Wealth Make Us Less Equal? The Role of Durable Goods in the Distribution of Wealth
We study the role an illiquid durable consumption good plays in determining the level of precautionary savings and the distribution of wealth in a standard Aiyagari model (i.e. a model with heterogeneous agents, idiosyncratic uncertainty, and borrowing constraints). Transactions costs induce an inaction region over which the durable stock and the associated user cost are not adjusted in response to changes in income, increasing, on average, the volatility of non-durable consumption. The volatility of total consumption is then a function of the share of the durable good in the utility function and the width of the inaction region. We are particularly interested in parameterizations which increase the precautionary motive for saving through an increase in "committed expenditure risk". We find, for an empirically relevant share of durable consumption and for all transaction costs below an upper threshold, that the level of precautionary savings is increasing in the transaction costs. Transaction costs have only a modest impact on the degree of wealth dispersion, as measured by the Gini index, as the associated increase in savings is close to linear in wealth. While we are unable to match the dispersion of wealth in the data, we increase the dispersion over a single asset model (Gini index of .71 for financial assets and .37 for total wealth) and we are able to match the relative dispersion of financial to durable assets, i.e. we find financial assets much more unequal than durable assets. We also match the ratio of housing wealth to total wealth for the median agent. We calibrate the model to data from the PSID, the CES, and the SCFPrecautionary Savings, Wealth Distribution, Durable Goods
Quadratization of Symmetric Pseudo-Boolean Functions
A pseudo-Boolean function is a real-valued function
of binary variables; that is, a mapping from
to . For a pseudo-Boolean function on
, we say that is a quadratization of if is a
quadratic polynomial depending on and on auxiliary binary variables
such that for
all . By means of quadratizations, minimization of is
reduced to minimization (over its extended set of variables) of the quadratic
function . This is of some practical interest because minimization of
quadratic functions has been thoroughly studied for the last few decades, and
much progress has been made in solving such problems exactly or heuristically.
A related paper \cite{ABCG} initiated a systematic study of the minimum number
of auxiliary -variables required in a quadratization of an arbitrary
function (a natural question, since the complexity of minimizing the
quadratic function depends, among other factors, on the number of
binary variables). In this paper, we determine more precisely the number of
auxiliary variables required by quadratizations of symmetric pseudo-Boolean
functions , those functions whose value depends only on the Hamming
weight of the input (the number of variables equal to ).Comment: 17 page
Liparu Lyetu - Our Life : Participatory Ethnographic Filmmaking in Applied Contexts.
This dissertation describes and critically assesses the production of the film Liparu Lyetu - Our Life . The documentary was made by a group of farmers in Northern Namibia in collaboration with anthropologist and filmmaker Martin Gruber. It depicts different forms of natural resource use and discusses related topics. The dissertation illustrates how the approach of Participatory Ethnographic Filmmaking was developed during the film's production and discusses how methods originating in Ethnographic Filmmaking and Participatory Video (PV) can contribute to both applied and academic research
The Lock-free -LSM Relaxed Priority Queue
Priority queues are data structures which store keys in an ordered fashion to
allow efficient access to the minimal (maximal) key. Priority queues are
essential for many applications, e.g., Dijkstra's single-source shortest path
algorithm, branch-and-bound algorithms, and prioritized schedulers.
Efficient multiprocessor computing requires implementations of basic data
structures that can be used concurrently and scale to large numbers of threads
and cores. Lock-free data structures promise superior scalability by avoiding
blocking synchronization primitives, but the \emph{delete-min} operation is an
inherent scalability bottleneck in concurrent priority queues. Recent work has
focused on alleviating this obstacle either by batching operations, or by
relaxing the requirements to the \emph{delete-min} operation.
We present a new, lock-free priority queue that relaxes the \emph{delete-min}
operation so that it is allowed to delete \emph{any} of the smallest
keys, where is a runtime configurable parameter. Additionally, the
behavior is identical to a non-relaxed priority queue for items added and
removed by the same thread. The priority queue is built from a logarithmic
number of sorted arrays in a way similar to log-structured merge-trees. We
experimentally compare our priority queue to recent state-of-the-art lock-free
priority queues, both with relaxed and non-relaxed semantics, showing high
performance and good scalability of our approach.Comment: Short version as ACM PPoPP'15 poste
Students with Disabilities: The Disconnect between Self Advocacy and Social Justice Practices of Teachers
This paper explored the perceptions of special education staff and college students with disabilities about self-advocacy instruction through the lens of social justice. Investigated were three public schools and one community college. Data revealed differing perceptions between educators and students regarding the level of self-advocacy instruction that students with disabilities received. The implications for this research and practice include that high school personnel understands and implements principles of social justice to teach students with disabilities to have self-advocacy skills
Optimum Centralized Portfolio Construction with Decentralized Portfolio Management
Many financial institutions employ outside portfolio managers to manage part or all of their investable assets. These institutions include pension funds, private endowments (e.g., colleges and charities), and private trusts. Pension funds are the largest and most likely organizations to employ several outside managers, each of whom manages a part of the overall portfolio. In this paper we will use the pension fund manager as the prototype of the centralized decision-maker trying to optimally manage a set of decentralized decision-makers but the analysts is general. If the centralized decision-maker (CDM) is a mean variance maximizer, the CDM could construct a portfolio using standard portfolio theory and estimates of mean return, variances, and covariances between the portfolios constructed by a group of decentralized managers. However, this overall portfolio is unlikely to be optimum since the individually managed portfolios themselves were constructed without taking into account the portfolios of the other managers. The purpose of this article is to set up a structure that leads to the optimum portfolio from the viewpoint of the CDM when there are multiple managers and their portfolios are constructed without reference to each other
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