447 research outputs found
Modeling Defaults In Banking & Real Estate
In this thesis, we study two topics related to defaults. First, we provide a Probability of Default (PD) calculation method for privately-held U.S. regional banks, using free and transparent data from the Federal Deposit Insurance Corporation (FDIC). Our method is efficient and useful for both investors and regulators. We have improved Moody's proprietary RiskCalc PD model [17] by creating a new cautionary index, which is able to capture default behaviors very well and has a very high predictive power over both one-year and six-month time horizons as shown by our numerical results. We also find that this performance is robust over different historical periods. We describe the factors we chose, the modeling methodology, and the model's accuracy in detail.
Second, we propose two strategies to reduce the frequency of defaults in home mortgages (foreclosures). The first is a new mortgage insurance contract (American put option with the house as the underlying asset). Our analysis differs from that for the standard put option in equity markets in that our strike (the remaining value of the mortgage) is time dependent, and the drift and volatility in the Geometric Brownian Motion are time dependent (step functions) due to a regime switch from declining to increasing house prices. Both theoretical derivations and numerical results will be obtained. We will also analyze the Adjustable Balance Mortgage (ABM) in continuous time as a second alternative to avoiding foreclosures. Here the mortgage payments are reduced if the house price falls below the remaining value of the mortgage
Materialized View Selection in XML Databases
Materialized views, a rdbms silver bullet, demonstrate its
efficacy in many applications, especially as a data warehousing/decison support system tool. The pivot of playing materialized views efficiently is view selection. Though studied for over thirty years in rdbms, the
selection is hard to make in the context of xml databases, where both the semi-structured data and the expressiveness of xml query languages add challenges to the view selection problem. We start our discussion on producing minimal xml views (in terms of size) as candidates for a given workload (a query set). To facilitate intuitionistic view selection, we present a view graph (called vcube) to structurally maintain all generated views. By basing our selection on vcube for materialization, we propose two view selection strategies, targeting at space-optimized and space-time tradeoff, respectively. We built our implementation on
top of Berkeley DB XML, demonstrating that significant performance improvement could be obtained using our proposed approaches
Multi-spectral image change detection based on single-band iterative weighting and fuzzy C-means clustering
Remarks on D_p and D_{p-2} with each carrying a flux
We explore various properties of interaction between D and D with
each carrying a worldvolume flux and with the -branes placed along
spatial worldvolume directions of the p-branes at a separation when . Carefully analyzing the annulus amplitudes calculated via the boundary
state approach, we find that many features of amplitudes remain similar to
those studied when such as the nature of force on the brane
separation, the onset of various instabilities when the brane-separation is on
the order of string scale and the occurrence of pair production of open strings
when there is a relevant electric flux present. In addition, we have also found
many new features of interaction which don't appear in the absence of fluxes or
when in the presence of fluxes, for examples, the nature of
interaction can be repulsive and there is no onset of tachyonic instability
under certain conditions. Even in the absence of a magnetic flux, we can have
an exponential enhancement of the rate of pair production of open strings in
certain cases, which may be significant enough to give observational
consequences.Comment: 15 pages, 3 tables, revised version to appear in PL
Di-hadron azimuthal correlation and Mach-like cone structure in parton/hadron transport model
In the framework of a multi-phase transport model (AMPT) with both partonic
and hadronic interactions, azimuthal correlations between trigger particles and
associated scattering particles have been studied by the mixing-event
technique. The momentum ranges of these particles are
GeV/ and GeV/ (soft), or 4
GeV/ and GeV/ (hard) in Au + Au collisions at
= 200 GeV. A Mach-like structure has been observed in
correlation functions for central collisions. By comparing scenarios with and
without parton cascade and hadronic rescattering, we show that both partonic
and hadronic dynamical mechanisms contribute to the Mach-like structure of the
associated particle azimuthal correlations. The contribution of hadronic
dynamical process can not be ignored in the emergence of Mach-like correlations
of the soft scattered associated hadrons. However, hadronic rescattering alone
cannot reproduce experimental amplitude of Mach-like cone on away-side, and the
parton cascade process is essential to describe experimental amplitude of
Mach-like cone on away-side. In addition, both the associated multiplicity and
the sum of decrease, whileas the increases, with the impact
parameter in the AMPT model including partonic dynamics from string melting
scenario.Comment: 9 pages, 5 figures; Physics Letters B 641, 362-367 (2006
Structure of Schlafen13 reveals a new class of tRNA/rRNA- targeting RNase engaged in translational control
Cleavage of transfer (t)RNA and ribosomal (r)RNA are critical and conserved steps of translational control for cells to overcome varied environmental stresses. However, enzymes that are responsible for this event have not been fully identified in high eukaryotes. Here, we report a mammalian tRNA/rRNA-targeting endoribonuclease: SLFN13, a member of the Schlafen family. Structural study reveals a unique pseudo-dimeric U-pillow-shaped architecture of the SLFN13 N'-domain that may clamp base-paired RNAs. SLFN13 is able to digest tRNAs and rRNAs in vitro, and the endonucleolytic cleavage dissevers 11 nucleotides from the 3'-terminus of tRNA at the acceptor stem. The cytoplasmically localised SLFN13 inhibits protein synthesis in 293T cells. Moreover, SLFN13 restricts HIV replication in a nucleolytic activity-dependent manner. According to these observations, we term SLFN13 RNase S13. Our study provides insights into the modulation of translational machinery in high eukaryotes, and sheds light on the functional mechanisms of the Schlafen family
A Statistical Study on Photospheric Magnetic Nonpotentiality of Active Regions and Its Relationship with Flares during Solar Cycles 22-23
A statistical study is carried out on the photospheric magnetic
nonpotentiality in solar active regions and its relationship with associated
flares. We select 2173 photospheric vector magnetograms from 1106 active
regions observed by the Solar Magnetic Field Telescope at Huairou Solar
Observing Station, National Astronomical Observatories of China, in the period
of 1988-2008, which covers most of the 22nd and 23rd solar cycles. We have
computed the mean planar magnetic shear angle (\bar{\Delta\phi}), mean shear
angle of the vector magnetic field (\bar{\Delta\psi}), mean absolute vertical
current density (\bar{|J_{z}|}), mean absolute current helicity density
(\bar{|h_{c}|}), absolute twist parameter (|\alpha_{av}|), mean free magnetic
energy density (\bar{\rho_{free}}), effective distance of the longitudinal
magnetic field (d_{E}), and modified effective distance (d_{Em}) of each
photospheric vector magnetogram. Parameters \bar{|h_{c}|}, \bar{\rho_{free}},
and d_{Em} show higher correlation with the evolution of the solar cycle. The
Pearson linear correlation coefficients between these three parameters and the
yearly mean sunspot number are all larger than 0.59. Parameters
\bar{\Delta\phi}, \bar{\Delta\psi}, \bar{|J_{z}|}, |\alpha_{av}|, and d_{E}
show only weak correlations with the solar cycle, though the nonpotentiality
and the complexity of active regions are greater in the activity maximum
periods than in the minimum periods. All of the eight parameters show positive
correlations with the flare productivity of active regions, and the combination
of different nonpotentiality parameters may be effective in predicting the
flaring probability of active regions.Comment: 20 pages, 5 figures, 4 tables, accepted for publication in Solar
Physic
Structural and morphological alterations induced by cobalt substitution in LaMnO3 perovskites
[EN] The chemical composition of a LaMnO3 perovskite was modified sequentially by an improved sol-gel method to include cobalt centers in some B sites formerly occupied by Mn. In this way, a representative set of materials of general formula LaMn1-xCoxO3 was obtained whose composition extends from LaMnO3 to LaCoO3. These perovskites, as promising materials for oxygen reduction or oxygen evolution reactions, were characterized by several imaging (SEM), spectroscopic (XPS, EDX) and diffraction (XRD) techniques to elucidate their structure and to demonstrate the existence of composition differences between the catalytic surface and the bulk material. Specifically, it was found that lanthanum ions prevail at the surface of the catalyst but high cobalt-substitution levels stimulate the surface enrichment in B cations in their respective higher oxidation states (Mn4+ and Co3+ against Mn3+ and Co2+). This phenomenon opens the possibility of tuning their electrocatalytic properties and to synthesize suitable materials for electrochemical reactions involving molecular oxygen. (C) 2019 Elsevier Inc. All rights reserved.The authors thank MINECO and FEDER (MAT2016-76595-R) for the financial support. J.X.F.-L. gratefully acknowledges MINECO for the financial support through FPI contract (BES-2017-081598).Flores-Lasluisa, JX.; Huerta, F.; Cazorla-Amoros, D.; Morallón, E. (2019). Structural and morphological alterations induced by cobalt substitution in LaMnO3 perovskites. Journal of Colloid and Interface Science. 556:658-666. https://doi.org/10.1016/j.jcis.2019.08.112S65866655
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