272 research outputs found
Tetris is Hard, Even to Approximate
In the popular computer game of Tetris, the player is given a sequence of
tetromino pieces and must pack them into a rectangular gameboard initially
occupied by a given configuration of filled squares; any completely filled row
of the gameboard is cleared and all pieces above it drop by one row. We prove
that in the offline version of Tetris, it is NP-complete to maximize the number
of cleared rows, maximize the number of tetrises (quadruples of rows
simultaneously filled and cleared), minimize the maximum height of an occupied
square, or maximize the number of pieces placed before the game ends. We
furthermore show the extreme inapproximability of the first and last of these
objectives to within a factor of p^(1-epsilon), when given a sequence of p
pieces, and the inapproximability of the third objective to within a factor of
(2 - epsilon), for any epsilon>0. Our results hold under several variations on
the rules of Tetris, including different models of rotation, limitations on
player agility, and restricted piece sets.Comment: 56 pages, 11 figure
CoVault: A Secure Analytics Platform
In a secure analytics platform, data sources consent to the exclusive use oftheir data for a pre-defined set of analytics queries performed by a specificgroup of analysts, and for a limited period. If the platform is secure under asufficiently strong threat model, it can provide the missing link to enablingpowerful analytics of sensitive personal data, by alleviating data subjects'concerns about leakage and misuse of data. For instance, many types of powerfulanalytics that benefit public health, mobility, infrastructure, finance, orsustainable energy can be made differentially private, thus alleviatingconcerns about privacy. However, no platform currently exists that issufficiently secure to alleviate concerns about data leakage and misuse; as aresult, many types of analytics that would be in the interest of data subjectsand the public are not done. CoVault uses a new multi-party implementation offunctional encryption (FE) for secure analytics, which relies on a uniquecombination of secret sharing, multi-party secure computation (MPC), anddifferent trusted execution environments (TEEs). CoVault is secure under a verystrong threat model that tolerates compromise and side-channel attacks on anyone of a small set of parties and their TEEs. Despite the cost of MPC, we showthat CoVault scales to very large data sizes using map-reduce based queryparallelization. For example, we show that CoVault can perform queries relevantto epidemic analytics at scale.<br
Controlling of Iridium films using interfacial proximity effects
High precision calorimetry using superconducting transition edge sensors
requires the use of superconducting films with a suitable , depending on
the application. To advance high-precision macrocalorimetry, we require
low- films that are easy to fabricate. A simple and effective way to
suppress of superconducting Iridium through the proximity effect is
demonstrated by using Ir/Pt bilayers as well as Au/Ir/Au trilayers. While Ir/Au
films fabricated by applying heat to the substrate during Ir deposition have
been used in the past for superconducting sensors, we present results of
suppression on Iridium by deposition at room temperature in Au/Ir/Au trilayers
and Ir/Pt bilayers in the range of 20-100~mK. Measurements of the
relative impedance between the Ir/Pt bilayers and Au/Ir/Au trilayers fabricated
show factor of 10 higher values in the Ir/Pt case. These new films could
play a key role in the development of scalable superconducting transition edge
sensors that require low- films to minimize heat capacity and maximize
energy resolution, while keeping high-yield fabrication methods.Comment: 5 journal pages, 4 figure
Controlling of Iridium Films Using the Proximity Effect
A superconducting Transition-Edge Sensor (TES) with low- is essential in
a high resolution calorimetric detection. With a motivation of developing
sensitive calorimeters for applications in cryogenic neutrinoless double beta
decay searches, we have been investigating methods to reduce the of an Ir
film down to 20 mK. Utilizing the proximity effect between a superconductor and
a normal metal, we found two room temperature fabrication recipes of making
Ir-based low- films. In the first approach, an Ir film sandwiched between
two Au films, a Au/Ir/Au trilayer, has a tunable in the range of 20-100
mK depending on the relative thicknesses. In the second approach, a
paramagnetic Pt thin film is used to create Ir/Pt bilayer with a tunable
in the same range. We present detailed study of fabrication and
characterization of Ir-based low- films, and compare the experimental
results to theoretical models. We show that Ir-based films with predictable and
reproducible critical temperature can be consistently fabricated for use in
large scale detector applications.Comment: 5 figures, accepted in the Journal of Applied Physic
Polyamorous Families – Parenting Practice, Stigma and Social Regulation
As a response to the greater visibility of alternative relationship and family forms, polyamory (i.e. the practice of consensual multi-partner relationships) has recently moved to the centre of public media attention. Questions of polyamory have emerged as a major concern within law, social policy, family sociology, gender and sexuality studies. Yet certain core issues have remained underexplored. This includes the distinctive nature of polyamorous intimacy, the structure of poly household formations and the dynamics of care work within poly families. In particular, poly parenting has been subject to tabooisation and scandalisation. Governing bodies, the judiciary and educational institutions have remained largely ignorant of polyamorous relationships. Research documents the exclusions of poly families (and individuals) from access to legal provisions and protections and their common discrimination in the courts, namely in custody cases. It further highlights the discrimination of polyidentified adolescents in school and college settings and the predicament that poly families face when interacting with public institutions (including schools and kindergardens). Insights into parenting practices and the organisation of childcare is vital for understanding the transformative potential of polyamorous ways of relating. It is also important for challenging the common demonisation and stigmatisation of polyamory within conservative family politics that perceives polyamory exclusively from a harm perspective. This paper will review and critically analyse existing research on poly parenting focussing on three dimensions: (a) parenting practices, (b) social and legal discrimination, and (c) parental response to stigmatisation. The paper argues for a stronger incorporation of queer perspectives within the guiding frameworks of research into parenting in consensually non-monogamous and polyamorous relationships to highlight the transformative potential of the ‘queer bonds’ that sustain many of these practices
Distal chromatin structure influences local nucleosome positions and gene expression
The positions of nucleosomes across the genome influence several cellular processes, including gene transcription. However, our understanding of the factors dictating where nucleosomes are located and how this affects gene regulation is still limited. Here, we perform an extensive in vivo study to investigate the influence of the neighboring chromatin structure on local nucleosome positioning and gene expression. Using truncated versions of the Saccharomyces cerevisiae URA3 gene, we show that nucleosome positions in the URA3 promoter are at least partly determined by the local DNA sequence, with so-called ‘antinucleosomal elements’ like poly(dA:dT) tracts being key determinants of nucleosome positions. In addition, we show that changes in the nucleosome positions in the URA3 promoter strongly affect the promoter activity. Most interestingly, in addition to demonstrating the effect of the local DNA sequence, our study provides novel in vivo evidence that nucleosome positions are also affected by the position of neighboring nucleosomes. Nucleosome structure may therefore be an important selective force for conservation of gene order on a chromosome, because relocating a gene to another genomic position (where the positions of neighboring nucleosomes are different from the original locus) can have dramatic consequences for the gene's nucleosome structure and thus its expression
Set Pseudophasors to Stun for Flow Cytometry
Study of signal transduction in live cells benefits from the ability to visualize and quantify light emitted by fluorescent proteins (XFPs) fused to different signaling proteins. However, because cell signaling proteins are often present in small numbers, and because the XFPs themselves are poor fluorophores, the amount of emitted light, and the observable signal in these studies, is often small. An XFP's fluorescence lifetime contains additional information about the immediate environment of the fluorophore that can augment the information from its weak light signal. Here, we constructed and expressed in Saccharomyces cerevisiae variants of Teal Fluorescent Protein (TFP) and Citrine that were isospectral but had shorter fluorescence lifetimes, ∼ 1.5 ns vs ∼ 3 ns. We modified microscopic and flow cytometric instruments to measure fluorescence lifetimes in live cells. We developed digital hardware and a measure of lifetime called a "pseudophasor" that we could compute quickly enough to permit sorting by lifetime in flow. We used these abilities to sort mixtures of cells expressing TFP and the short-lifetime TFP variant into subpopulations that were respectively 97% and 94% pure. This work demonstrates the feasibility of using information about fluorescence lifetime to help quantify cell signaling in living cells at the high throughput provided by flow cytometry. Moreover, it demonstrates the feasibility of isolating and recovering subpopulations of cells with different XFP lifetimes for subsequent experimentation
Growth landscape formed by perception and import of glucose in yeast
An important challenge in systems biology is to quantitatively describe microbial growth using a few measurable parameters that capture the essence of this complex phenomenon. Two key events at the cell membrane—extracellular glucose sensing and uptake—initiate the budding yeast’s growth on glucose. However, conventional growth models focus almost exclusively on glucose uptake. Here we present results from growth-rate experiments that cannot be explained by focusing on glucose uptake alone. By imposing a glucose uptake rate independent of the sensed extracellular glucose level, we show that despite increasing both the sensed glucose concentration and uptake rate, the cell’s growth rate can decrease or even approach zero. We resolve this puzzle by showing that the interaction between glucose perception and import, not their individual actions, determines the central features of growth, and characterize this interaction using a quantitative model. Disrupting this interaction by knocking out two key glucose sensors significantly changes the cell’s growth rate, yet uptake rates are unchanged. This is due to a decrease in burden that glucose perception places on the cells. Our work shows that glucose perception and import are separate and pivotal modules of yeast growth, the interaction of which can be precisely tuned and measured.National Institutes of Health (U.S.). Pioneer AwardNatural Sciences and Engineering Research Council of Canada (NSERC). Graduate Fellowshi
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