5,272 research outputs found
Response Of The Dupi Tila Aquifer to intensive pumping in Dhaka, Bangladesh
This paper focuses on the water-quantity issues facing Dhaka because of the rapid exploitation of the Dupi Tila aquifer. Dhaka is one of the world’s largest groundwater-dependent cities, relying on water withdrawn from this underlying semiconfined sand aquifer. A meteoric rise in well construction in both the private and public sectors in recent years has produced an estimated 1,300 boreholes that tap the aquifer in urban and suburban parts of the city. Analysis of construction records for public-supply wells drilled between 1970 and 2000 shows that water levels are falling in several areas of the city despite apparently favorable recharge conditions . The productivity of boreholes as measured by specific capacity has also declined significantly. Even though the aquifer system is vital to the infrastructure of the city it remains a poorly quantified resource, and until this is resolved by investment in evaluation studies, attempts to efficiently manage the resource in a sustainable way will be frustrated
Changing vegetation patterns in Yobe State Nigeria:an analysis of the rates of change, potential causes and the implications for sustainable resource management
Impact of US Macroeconomic Surprises on Stock Market Returns in Developed Economies
Macroeconomic conditions are known to affect risks factors and thereby influence asset returns within a given economy. We explore this link in a global setting. Given the dominant role the U.S. economy plays in the global economic environment, U.S. Macro economic shocks are expected to affect asset returns in other countries. The impact should be more pronounced in the developed economies where the U.S. is a large trading and capital-flows partner. Our results shows that residual returns and conditional volatilities in major developed economies are significantly impacted by US macroeconomic surprises. We identify U.S. macro economic shocks that have spillover impact on global asset returns over and above those transmitted through equity market returns. While return levels are significantly influenced by productivity and retail sales surprises, return conditional volatilities are mainly influenced by inflation, personal income, industrial production, leading indicators, and gross domestic product surprises.
Cd3As2 is Centrosymmetric
This is a revised version of a manuscript that was originally posted here in
February of 2014. It has been accepted at the journal Inorganic Chemistry after
reviews that included those of two crystallographers who made sure all the t's
were crossed and the i's were dotted. The old work (from 1968) that said that
Cd3As2 was noncentrosymmetric was mistaken, with the authors of that study
making a type of error that in the 1980s became infamous in crystallography. As
a result of the increased scrutiny of the issue of centrosymmetricity of the
1980's, there are now much better analysis tools to resolve the issue fully,
and its important to understand that not just our crystals are centrosymmetric,
even the old guy's crystals were centrosymmetric (and by implication everyone's
are). There is no shame in having made that error back in the day and those
authors would not find the current centrosymmetric result controversial; their
paper is excellent in all other aspects. This manuscript describes how the
structure is determined, explains the structure schematically, calculates the
electronic structure based on the correct centrosymmetric crystal structure,
and gives the structural details that should be used for future analysis and
modeling.Comment: Accepted by ACS Inorganic Chemistr
Learning to Approximate a Bregman Divergence
Bregman divergences generalize measures such as the squared Euclidean
distance and the KL divergence, and arise throughout many areas of machine
learning. In this paper, we focus on the problem of approximating an arbitrary
Bregman divergence from supervision, and we provide a well-principled approach
to analyzing such approximations. We develop a formulation and algorithm for
learning arbitrary Bregman divergences based on approximating their underlying
convex generating function via a piecewise linear function. We provide
theoretical approximation bounds using our parameterization and show that the
generalization error for metric learning using our framework
matches the known generalization error in the strictly less general Mahalanobis
metric learning setting. We further demonstrate empirically that our method
performs well in comparison to existing metric learning methods, particularly
for clustering and ranking problems.Comment: 19 pages, 4 figure
External Momentum, Volume Effects, and the Nucleon Magnetic Moment
We analyze the determination of volume effects for correlation functions that
depend on an external momentum. As a specific example, we consider finite
volume nucleon current correlators, and focus on the nucleon magnetic moment.
Because the multipole decomposition relies on SO(3) rotational invariance, the
structure of such finite volume corrections is unrelated to infinite volume
multipole form factors. One can deduce volume corrections to the magnetic
moment only when a zero-mode photon coupling vanishes, as occurs at
next-to-leading order in heavy baryon chiral perturbation theory. To deduce
such finite volume corrections, however, one must assume continuous momentum
transfer. In practice, volume corrections with momentum transfer dependence are
required to address the extraction of the magnetic moment, or other observables
that arise in momentum dependent correlation functions. Additionally we shed
some light on a puzzle concerning differences in lattice form factor data at
equal values of momentum transfer squared.Comment: 21 pages, 5 figures; discussion in Sect. IV C expanded, Figs. now B&W
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Cost-effectiveness of traffic enforcement: case study from Uganda
BACKGROUND:
In October 2004, the Ugandan Police department deployed enhanced traffic safety patrols on the four major roads to the capital Kampala.
OBJECTIVE:
To assess the costs and potential effectiveness of increasing traffic enforcement in Uganda.
METHODS:
Record review and key informant interviews were conducted at 10 police stations along the highways that were patrolled. Monthly data on traffic citations and casualties were reviewed for January 2001 to December 2005; time series (ARIMA) regression was used to assess for a statistically significant change in traffic deaths. Costs were computed from the perspective of the police department in 72,000. Since deployment, the number of citations has increased substantially with a value of 603 per death averted or 300 GDP per capita).
CONCLUSION:
The costs of traffic safety enforcement are low in comparison to the potential number of lives saved and revenue generated. Increasing enforcement of existing traffic safety norms can prove to be an extremely cost-effective public health intervention in low-income countries, even from a government perspective
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