16,431 research outputs found
Economic choices can be made using only stimulus values
Decision-making often involves choices between different stimuli, each of which is associated with a different physical action. A growing consensus suggests that the brain makes such decisions by assigning a value to each available option and then comparing them to make a choice. An open question in decision neuroscience is whether the brain computes these choices by comparing the values of stimuli directly in goods space or instead by first assigning values to the associated actions and then making a choice over actions. We used a functional MRI paradigm in which human subjects made choices between different stimuli with and without knowledge of the actions required to obtain the different stimuli. We found neural correlates of the value of the chosen stimulus (a postdecision signal) in ventromedial prefrontal cortex before the actual stimulus–action pairing was revealed. These findings provide support for the hypothesis that the brain is capable of making choices in the space of goods without first transferring values into action space
Computing canonical heights using arithmetic intersection theory
For several applications in the arithmetic of abelian varieties it is
important to compute canonical heights. Following Faltings and Hriljac, we show
how the canonical height on the Jacobian of a smooth projective curve can be
computed using arithmetic intersection theory on a regular model of the curve
in practice. In the case of hyperelliptic curves we present a complete
algorithm that has been implemented in Magma. Several examples are computed and
the behavior of the running time is discussed.Comment: 29 pages. Fixed typos and minor errors, restructured some sections.
Added new Example
Computing Genus-Zero Twisted Gromov-Witten Invariants
Twisted Gromov-Witten invariants are intersection numbers in moduli spaces of
stable maps to a manifold or orbifold X which depend in addition on a vector
bundle over X and an invertible multiplicative characteristic class. Special
cases are closely related to local Gromov-Witten invariants of the bundle, and
to genus-zero one-point invariants of complete intersections in X. We develop
tools for computing genus-zero twisted Gromov-Witten invariants of orbifolds
and apply them to several examples. We prove a "quantum Lefschetz theorem"
which expresses genus-zero one-point Gromov-Witten invariants of a complete
intersection in terms of those of the ambient orbifold X. We determine the
genus-zero Gromov-Witten potential of the type A surface singularity C^2/Z_n.
We also compute some genus-zero invariants of C^3/Z_3, verifying predictions of
Aganagic-Bouchard-Klemm. In a self-contained Appendix, we determine the
relationship between the quantum cohomology of the A_n surface singularity and
that of its crepant resolution, thereby proving the Crepant Resolution
Conjectures of Ruan and Bryan-Graber in this case.Comment: 46 pages. v2: corrected our description of the work of Davesh Maulik.
v3 is the refereed version, with many changes: a new appendix containing the
results from our preprint arXiv:0704.2034; another new appendix containing
foundational results on Givental's Lagrangian cone and formal geometry; also
a number of typos were corrected and some references adde
Prediction of secondary structures for large RNA molecules
The prediction of correct secondary structures of large RNAs is one of the unsolved challenges of computational molecular biology. Among the major obstacles is the fact that accurate calculations scale as O(n⁴), so the computational requirements become prohibitive as the length increases. We present a new parallel multicore and scalable program called GTfold, which is one to two orders of magnitude faster than the de facto standard programs mfold and RNAfold for folding large RNA viral sequences and achieves comparable accuracy of prediction. We analyze the algorithm's concurrency and describe the parallelism for a shared memory environment such as a symmetric multiprocessor or multicore chip. We are seeing a paradigm shift to multicore chips and parallelism must be explicitly addressed to continue gaining performance with each new generation of systems.
We provide a rigorous proof of correctness of an optimized algorithm for internal loop calculations called internal loop speedup algorithm (ILSA), which reduces the time complexity of internal loop computations from O(n⁴) to O(n³) and show that the exact algorithms such as ILSA are executed with our method in affordable amount of time. The proof gives insight into solving these kinds of combinatorial problems. We have documented detailed pseudocode of the algorithm for predicting minimum free energy secondary structures which provides a base to implement future algorithmic improvements and improved thermodynamic model in GTfold. GTfold is written in C/C++ and freely available as open source from our website.M.S.Committee Chair: Bader, David; Committee Co-Chair: Heitsch, Christine; Committee Member: Harvey, Stephen; Committee Member: Vuduc, Richar
Relational quantum computing using only maximally mixed initial qubit states
We disprove the conjecture of [1], namely that it would require smarter
authors to find a way of making the two-qubit singlet/triplet measurement
quantum computationally universal given an ensemble of initial single qubit
states with less than three linearly independent Bloch vectors. We show, in
fact, that an initial ensemble of maximally mixed single qubits suffices.Comment: 2 + epsilon page
Recursion formulae of higher Weil-Petersson volumes
In this paper we study effective recursion formulae for computing
intersection numbers of mixed and classes on moduli spaces of
curves. By using the celebrated Witten-Kontsevich theorem, we generalize
Mulase-Safnuk form of Mirzakhani's recursion and prove a recursion formula of
higher Weil-Petersson volumes. We also present recursion formulae to compute
intersection pairings in the tautological rings of moduli spaces of curves.Comment: 18 pages, to appear in IMR
Evaluative Conditioning: Arti-fact or -fiction?—A Reply to Baeyens, De Houwer, Vansteenwegen, and Eelen (1998)
Baeyens et al.(1998) claim that Field and Davey's (1997) controversial study of conceptual conditioning offers little threat to current conceptions of evaluative conditioning. This article addresses some of the questions posed by Baeyenset al.First, some criticisms of the conceptual conditioning study appear to be based on a misunderstanding of the procedure. Second, we address the issues surrounding the so-called Type-X procedure. Specifically, we begin by reviewing the status of studies that have used a procedure different from the Type-X procedure. It is then argued that, although the Type-X procedure has been used in only a portion of EC research, it has been used primarily in those studies whose outcome has been used to argue that evaluative conditioning (EC) is functionally distinct from autonomic conditioning. We then review the evidence from non-Type-X procedures that EC is a distinct form of learning. Finally, an attempt is made to explain why between-subject controls should be used as a matter of course in this field of research
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