14,255 research outputs found
Nonparametric estimation of a convex bathtub-shaped hazard function
In this paper, we study the nonparametric maximum likelihood estimator (MLE)
of a convex hazard function. We show that the MLE is consistent and converges
at a local rate of at points where the true hazard function is
positive and strictly convex. Moreover, we establish the pointwise asymptotic
distribution theory of our estimator under these same assumptions. One notable
feature of the nonparametric MLE studied here is that no arbitrary choice of
tuning parameter (or complicated data-adaptive selection of the tuning
parameter) is required.Comment: Published in at http://dx.doi.org/10.3150/09-BEJ202 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Estimation of a discrete monotone distribution
We study and compare three estimators of a discrete monotone distribution:
(a) the (raw) empirical estimator; (b) the "method of rearrangements"
estimator; and (c) the maximum likelihood estimator. We show that the maximum
likelihood estimator strictly dominates both the rearrangement and empirical
estimators in cases when the distribution has intervals of constancy. For
example, when the distribution is uniform on , the asymptotic
risk of the method of rearrangements estimator (in squared norm) is
, while the asymptotic risk of the MLE is of order .
For strictly decreasing distributions, the estimators are asymptotically
equivalent.Comment: 39 pages. See also
http://www.stat.washington.edu/www/research/reports/2009/
http://www.stat.washington.edu/jaw/RESEARCH/PAPERS/available.htm
High isolation RF signal selection switches
A selection switch with high isolation between RF signal input terminals is achieved with a gated Schmitt trigger circuit feeding into a control NAND gate in each signal switching channel. The control NAND gates of the separate signal channels are coupled to an output terminal by a single NAND gate. The schmitt trigger circuits and all gates are implemented with Schottky transistor-transistor logic circuits having input clamping diodes. Each Schmitt trigger circuit includes two cascaded NAND gates and a feedback isolation Schottky diode between one input terminal connected to receive an RF input and another input terminal connected to receive a feedback signal from the second of the two cascaded NAND gates. Both NAND gates of the Schmitt trigger circuits are enabled by the same switch control signal which enables the control gates
Cities as emergent models: the morphological logic of Manhattan and Barcelona
This paper is set to unveil several particulars about the logic embedded in the diachronic model of city
growth and the rules which govern the emergence of urban spaces. The paper outlines an attempt to
detect and define the generative rules of a growing urban structure by means of evaluation techniques.
The initial approach in this regards will be to study the evolution of existing urban regions or cities which
in our case are Manhattan and Barcelona and investigate the rules and causes of their emergence and
growth. The paper will concentrate on the spatial aspect of the generative rules and investigate their
behaviour and dimensionality. Several Space Syntax evaluation methods will be implemented to capture
the change of spatial configurations within the growing urban structures. In addition, certain spatial
elements will be isolated and tested aiming to illustrate their influence on the main spatial structures.
Both urban regions were found to be emergent products of a bottom up organic growth mostly
distinguished in the vicinities of the first settlements. Despite the imposition of a uniform grid on both
cities in later stages of their development these cities managed to deform the regularity in the preplanned
grid in an emergent manner to end up with an efficient model embodied in their current spatial
arrangement. The paper reveals several consistencies in the spatial morphology of both urban regions
and provides explanation of these regularities in an approach to extract the underlying rules which
contributed to the growth optimization process
Ultrasonic detection of flaws in fusion butt welds
Reliable and accurate Delta technique, a nondestructive ultrasonics method, uses redirection of energy to detect randomly oriented imperfections in fusion butt welds. Data on flaws can be read from either an oscilloscope or a printout
European social workers in England: exploring international labour mobility
Social work is generally regarded as an essentially ‘local activity’ but it is increasingly acknowledged that European and international trends have a bearing on development of national services and practices. This extends to the mobility of social workers themselves and England has experienced a steady growth in the recruitment of ‘international social workers’ who were born and qualified elsewhere. This is a generally under-researched area but the authors have drawn on literature in the wider field of labour migration and also secondary data and anecdotal evidence to present some facts and ideas about recruitment as it applies to social workers from European Union (EU) member states in particular. International social workers come to England from a large number and wide range of countries. However, the balance has been shifting between recruitment predominantly from the US and Commonwealth countries to a greater number from EU states. The current characteristics of international (particularly EU) social work recruitment are outlined in this paper and reasons related to both (national) demand and (international) supply are suggested. It is proposed that reasons are related to changes and conditions in the EU; to the national Government’s efforts to curb immigration; and to the particular characteristics of social work employment in England, particularly in child protection work. Some of the implications for European social workers of working in England are explored and it is concluded that there is a need for comparative and transnational research in this field
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