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Abstract Proper celltype identity relies on highly coordinated regulation of gene expression. Regulatory elements such as enhancers can produce cell typespecific expression patterns, but the mechanisms underlying specificity are not well understood. We previously identified an enhancer region capable of driving specific expression in giant cells, which are large, highly endoreduplicated cells in the Arabidopsis thaliana sepal epidermis. In this study, we use the giant cell enhancer as a model to understand the regulatory logic that promotes cell typespecific expression. Our dissection of the enhancer revealed that giant cell specificity is mediated primarily through the combination of two activators and one repressor. HDZIP and TCP transcription factors are involved in the activation of expression throughout the epidermis. High expression of HDZIP transcription factor genes in giant cells promoted higher expression driven by the enhancer in giant cells. Dof transcription factors repressed the activity of the enhancer such that only giant cells maintained enhancer activity. Thus, our data are consistent with a conceptual model whereby cell typespecific expression emerges from the combined activities of three transcription factor families activating and repressing expression in epidermal cells.more » « lessFree, publiclyaccessible full text available February 23, 2024

Memoryhard functions (MHFs) are a key cryptographic primitive underlying the design of moderately expensive password hashing algorithms and egalitarian proofs of work. Over the past few years several increasingly stringent goals for an MHF have been proposed including the requirement that the MHF have high sequential spacetime (ST) complexity, parallel spacetime complexity, amortized areatime (aAT) complexity and sustained space complexity. DataIndependent Memory Hard Functions (iMHFs) are of special interest in the context of password hashing as they naturally resist sidechannel attacks. iMHFs can be specified using a directed acyclic graph (DAG) $G$ with $N=2^n$ nodes and low indegree and the complexity of the iMHF can be analyzed using a pebbling game. Recently, Alwen et al. [CCS'17] constructed an DAG called DRSample which has aAT complexity at least $\Omega\left( N^2/\log N\right)$. Asymptotically DRSample outperformed all prior iMHF constructions including Argon2i, winner of the password hashing competition (aAT cost $\mathcal{O}\left(N^{1.767}\right)$), though the constants in these bounds are poorly understood. We show that the the greedy pebbling strategy of Boneh et al. [ASIACRYPT'16] is particularly effective against DRSample e.g., the aAT cost is $\mathcal{O}\left( N^2/\log N\right)$. In fact, our empirical analysis {\em reverses} the prior conclusion of Alwen et al. that DRSample provides stronger resistance to known pebbling attacks for practical values of $N \leq 2^{24}$. We construct a new iMHF candidate (DRSample+BRG) by using the bitreversal graph to extend DRSample. We then prove that the construction is asymptotically optimal under every MHF criteria, and we empirically demonstrate that our iMHF provides the best resistance to {\em known} pebbling attacks. For example, we show that any parallel pebbling attack either has aAT cost $\omega(N^2)$ or requires at least $\Omega(N)$ steps with $\Omega(N/\log N)$ pebbles on the DAG. This makes our construction the first practical iMHF with a strong sustained spacecomplexity guarantee and immediately implies that any parallel pebbling has aAT complexity $\Omega(N^2/\log N)$. We also prove that any sequential pebbling (including the greedy pebbling attack) has aAT cost $\Omega\left( N^2\right)$ and, if a plausible conjecture holds, any parallel pebbling has aAT cost $\Omega(N^2 \log \log N/\log N)$  the best possible bound for an iMHF. We implement our new iMHF and demonstrate that it is just as fast as Argon2. Along the way we propose a simple modification to the Argon2 round function which increases an attacker's aAT cost by nearly an order of magnitude without increasing running time on a CPU. Finally, we give a pebbling reduction which proves that in the parallel random oracle model (PROM) the cost of evaluating an iMHF like Argon2i or DRSample+BRG is given by the pebbling cost of the underlying DAG. Prior pebbling reductions assumed that the iMHF round function concatenates input labels before hashing and did not apply to practical iMHFs such as Argon2i, DRSample or DRSample+BRG where input labels are instead XORed together.more » « less

Free, publiclyaccessible full text available June 1, 2024

Free, publiclyaccessible full text available May 1, 2024

A bstract A search for Higgs boson pair production in events with two b jets and two τ leptons is presented, using a proton–proton collision dataset with an integrated luminosity of 139 fb − 1 collected at $$ \sqrt{s} $$ s = 13 TeV by the ATLAS experiment at the LHC. Higgs boson pairs produced nonresonantly or in the decay of a narrow scalar resonance in the mass range from 251 to 1600 GeV are targeted. Events in which at least one τ lepton decays hadronically are considered, and multivariate discriminants are used to reject the backgrounds. No significant excess of events above the expected background is observed in the nonresonant search. The largest excess in the resonant search is observed at a resonance mass of 1 TeV, with a local (global) significance of 3 . 1 σ (2 . 0 σ ). Observed (expected) 95% confidencelevel upper limits are set on the nonresonant Higgs boson pairproduction crosssection at 4.7 (3.9) times the Standard Model prediction, assuming Standard Model kinematics, and on the resonant Higgs boson pairproduction crosssection at between 21 and 900 fb (12 and 840 fb), depending on the mass of the narrow scalar resonance.more » « lessFree, publiclyaccessible full text available July 1, 2024

A bstract A combination of measurements of the inclusive topquark pair production crosssection performed by ATLAS and CMS in proton–proton collisions at centreofmass energies of 7 and 8 TeV at the LHC is presented. The crosssections are obtained using topquark pair decays with an oppositecharge electron–muon pair in the final state and with data corresponding to an integrated luminosity of about 5 fb − 1 at $$ \sqrt{s} $$ s = 7 TeV and about 20 fb − 1 at $$ \sqrt{s} $$ s = 8 TeV for each experiment. The combined crosssections are determined to be 178 . 5 ± 4 . 7 pb at $$ \sqrt{s} $$ s = 7 TeV and $$ {243.3}_{5.9}^{+6.0} $$ 243.3 − 5.9 + 6.0 pb at $$ \sqrt{s} $$ s = 8 TeV with a correlation of 0.41, using a reference topquark mass value of 172.5 GeV. The ratio of the combined crosssections is determined to be R 8 / 7 = 1 . 363 ± 0 . 032. The combined measured crosssections and their ratio agree well with theory calculations using several parton distribution function (PDF) sets. The values of the topquark pole mass (with the strong coupling fixed at 0.118) and the strong coupling (with the topquark pole mass fixed at 172.5 GeV) are extracted from the combined results by fitting a nexttonexttoleadingorder plus nexttonexttoleadinglog QCD prediction to the measurements. Using a version of the NNPDF3.1 PDF set containing no topquark measurements, the results obtained are $$ {m}_t^{\textrm{pole}}={173.4}_{2.0}^{+1.8} $$ m t pole = 173.4 − 2.0 + 1.8 GeV and $$ {\alpha}_{\textrm{s}}\left({m}_Z\right)={0.1170}_{0.0018}^{+0.0021} $$ α s m Z = 0.1170 − 0.0018 + 0.0021 .more » « lessFree, publiclyaccessible full text available July 1, 2024