422 research outputs found
Modeling tax evasion with genetic algorithms
The U.S. tax gap is estimated to exceed $450 billion, most of which arises from non-compliance on the part of individual taxpayers (GAO 2012; IRS 2006). Much is hidden in innovative tax shelters combining multiple business structures such as partnerships, trusts, and S-corporations into complex transaction networks designed to reduce and obscure the true tax liabilities of their individual shareholders. One known gambit employed by these shelters is to offset real gains in one part of a portfolio by creating artificial capital losses elsewhere through the mechanism of âinflated basisâ (TaxAnalysts 2005), a process made easier by the relatively flexible set of rules surrounding âpass-throughâ entities such as partnerships (IRS 2009). The ability to anticipate the likely forms of emerging evasion schemes would help auditors develop more efficient methods of reducing the tax gap. To this end, we have developed a prototype evolutionary algorithm designed to generate potential schemes of the inflated basis type described above. The algorithm takes as inputs a collection of asset types and tax entities, together with a rule-set governing asset exchanges between these entities. The schemes produced by the algorithm consist of sequences of transactions within an ownership network of tax entities. Schemes are ranked according to a âfitness functionâ (Goldberg in Genetic algorithms in search, optimization, and machine learning. Addison-Wesley, Boston, 1989); the very best schemes are those that afford the highest reduction in tax liability while incurring the lowest expected penalty.Mitre Corporation (Innovation Program
A New Architecture for DNAâTemplated Synthesis in Which Abasic Sites Protect Reactants from Degradation
The synthesis of artificial sequenceâdefined polymers that match and extend the functionality of proteins is an important goal in materials science. One way of achieving this is to program a sequence of chemical reactions between precursor building blocks by means of attached oligonucleotide adapters. However, hydrolysis of the reactive building blocks has so far limited the length and yield of product that can be obtained using DNAâtemplated reactions. Here, we report an architecture for DNAâtemplated synthesis in which reactants are tethered at internal abasic sites on opposite strands of a DNA duplex. We show that an abasic site within a DNA duplex can protect a nearby thioester from degradation, significantly increasing the yield of a DNAâtemplated reaction. This protective effect has the potential to overcome the challenges associated with programmable, sequenceâcontrolled synthesis of long nonânatural polymers by extending the lifetime of the reactive building blocks
A New Architecture for DNAâTemplated Synthesis in Which Abasic Sites Protect Reactants from Degradation
The synthesis of artificial sequenceâdefined polymers that match and extend the functionality of proteins is an important goal in materials science. One way of achieving this is to program a sequence of chemical reactions between precursor building blocks by means of attached oligonucleotide adapters. However, hydrolysis of the reactive building blocks has so far limited the length and yield of product that can be obtained using DNAâtemplated reactions. Here, we report an architecture for DNAâtemplated synthesis in which reactants are tethered at internal abasic sites on opposite strands of a DNA duplex. We show that an abasic site within a DNA duplex can protect a nearby thioester from degradation, significantly increasing the yield of a DNAâtemplated reaction. This protective effect has the potential to overcome the challenges associated with programmable, sequenceâcontrolled synthesis of long nonânatural polymers by extending the lifetime of the reactive building blocks
MaRCoS, an open-source electronic control system for low-field MRI
Every magnetic resonance imaging (MRI) device requires an electronic control
system that handles pulse sequences and signal detection and processing. Here
we provide details on the architecture and performance of MaRCoS, a MAgnetic
Resonance COntrol System developed by an open international community of
low-field MRI researchers. MaRCoS is inexpensive and can handle cycle-accurate
sequences without hard length limitations, rapid bursts of events, and
arbitrary waveforms. It can also be easily adapted to meet further
specifications required by the various academic and private institutions
participating in its development. We describe the MaRCoS hardware, firmware and
software that enable all of the above, including a Python-based graphical user
interface for pulse sequence implementation, data processing and image
reconstruction.Comment: 10 pages, 4 figure
"He was shot because america will not give up on racism":Martin Luther King Jr. And the african american civil rights movement in British schools
This article examines how Martin Luther King Jr. and the movement with which he is often synonymous are taught in UK schools, as well as the consequences of that teaching for twenty-first-century understandings of Britain's racial past and present. The UK's King-centric approach to teaching the civil rights movement has much in common with that in the US, including an inattention to its transnational coordinates. However, these shared (mis)representations have different histories, are deployed to different ends, and have different consequences. In the UK, study of the African American freedom struggle often happens in the absence of, and almost as a surrogate for, engagement with the histories of Britain's own racial minorities and imperial past. In short, emphasis on the apparent singularity of US race relations and the achievements of the mid-twentieth-century African American freedom struggle facilitates cultural amnesia regarding the historic and continuing significance of race and racism in the UK. In light of the Windrush scandal and the damning 2018 Royal Historical Society report on âRace, Ethnicity and Equality in UK History,â this article argues both for better, more nuanced and more relevant teaching of King and the freedom struggle in British schools, and for much greater attention to black British history in its own right
Identification of polymorphic inversions from genotypes
Background: Polymorphic inversions are a source of genetic variability with a direct impact on recombination frequencies. Given the difficulty of their experimental study, computational methods have been developed to infer their existence in a large number of individuals using genome-wide data of nucleotide variation. Methods based on haplotype tagging of known inversions attempt to classify individuals as having a normal or inverted allele. Other methods that measure differences between linkage disequilibrium attempt to identify regions with inversions but unable to classify subjects accurately, an essential requirement for association studies. Results: We present a novel method to both identify polymorphic inversions from genome-wide genotype data and classify individuals as containing a normal or inverted allele. Our method, a generalization of a published method for haplotype data [1], utilizes linkage between groups of SNPs to partition a set of individuals into normal and inverted subpopulations. We employ a sliding window scan to identify regions likely to have an inversion, and accumulation of evidence from neighboring SNPs is used to accurately determine the inversion status of each subject. Further, our approach detects inversions directly from genotype data, thus increasing its usability to current genome-wide association studies (GWAS). Conclusions: We demonstrate the accuracy of our method to detect inversions and classify individuals on principled-simulated genotypes, produced by the evolution of an inversion event within a coalescent model [2]. We applied our method to real genotype data from HapMap Phase III to characterize the inversion status of two known inversions within the regions 17q21 and 8p23 across 1184 individuals. Finally, we scan the full genomes of the European Origin (CEU) and Yoruba (YRI) HapMap samples. We find population-based evidence for 9 out of 15 well-established autosomic inversions, and for 52 regions previously predicted by independent experimental methods in ten (9+1) individuals [3,4]. We provide efficient implementations of both genotype and haplotype methods as a unified R package inveRsion
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Upper limits on the strength of periodic gravitational waves from PSR J1939+2134
The first science run of the LIGO and GEO gravitational wave detectors
presented the opportunity to test methods of searching for gravitational waves
from known pulsars. Here we present new direct upper limits on the strength of
waves from the pulsar PSR J1939+2134 using two independent analysis methods,
one in the frequency domain using frequentist statistics and one in the time
domain using Bayesian inference. Both methods show that the strain amplitude at
Earth from this pulsar is less than a few times .Comment: 7 pages, 1 figure, to appear in the Proceedings of the 5th Edoardo
Amaldi Conference on Gravitational Waves, Tirrenia, Pisa, Italy, 6-11 July
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Improving the sensitivity to gravitational-wave sources by modifying the input-output optics of advanced interferometers
We study frequency dependent (FD) input-output schemes for signal-recycling
interferometers, the baseline design of Advanced LIGO and the current
configuration of GEO 600. Complementary to a recent proposal by Harms et al. to
use FD input squeezing and ordinary homodyne detection, we explore a scheme
which uses ordinary squeezed vacuum, but FD readout. Both schemes, which are
sub-optimal among all possible input-output schemes, provide a global noise
suppression by the power squeeze factor, while being realizable by using
detuned Fabry-Perot cavities as input/output filters. At high frequencies, the
two schemes are shown to be equivalent, while at low frequencies our scheme
gives better performance than that of Harms et al., and is nearly fully
optimal. We then study the sensitivity improvement achievable by these schemes
in Advanced LIGO era (with 30-m filter cavities and current estimates of
filter-mirror losses and thermal noise), for neutron star binary inspirals, and
for narrowband GW sources such as low-mass X-ray binaries and known radio
pulsars. Optical losses are shown to be a major obstacle for the actual
implementation of these techniques in Advanced LIGO. On time scales of
third-generation interferometers, like EURO/LIGO-III (~2012), with
kilometer-scale filter cavities, a signal-recycling interferometer with the FD
readout scheme explored in this paper can have performances comparable to
existing proposals. [abridged]Comment: Figs. 9 and 12 corrected; Appendix added for narrowband data analysi
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