TY - JOUR
AB - We investigate the effects of a magnetic field on the dynamics of rotationally inelastic collisions of open-shell molecules (Σ2, Σ3, and Π2) with closed-shell atoms. Our treatment makes use of the Fraunhofer model of matter wave scattering and its recent extension to collisions in electric [M. Lemeshko and B. Friedrich, J. Chem. Phys. 129, 024301 (2008)] and radiative fields [M. Lemeshko and B. Friedrich, Int. J. Mass. Spec. 280, 19 (2009)]. A magnetic field aligns the molecule in the space-fixed frame and thereby alters the effective shape of the diffraction target. This significantly affects the differential and integral scattering cross sections. We exemplify our treatment by evaluating the magnetic-field-dependent scattering characteristics of the He-CaH (XΣ+2), He-O2 (XΣ–3), and He-OH (XΠΩ2) systems at thermal collision energies. Since the cross sections can be obtained for different orientations of the magnetic field with respect to the relative velocity vector, the model also offers predictions about the frontal-versus-lateral steric asymmetry of the collisions. The steric asymmetry is found to be almost negligible for the He-OH system, weak for the He-CaH collisions, and strong for the He-O2. While odd ΔM transitions dominate the He-OH [J=3/2,f→J′,e/f] integral cross sections in a magnetic field parallel to the relative velocity vector, even ΔM transitions prevail in the case of the He-CaH (X2Σ+) and He-O2 (XΣ−3) collision systems. For the latter system, the magnetic field opens inelastic channels that are closed in the absence of the field. These involve the transitions N=1,J=0→N′, J′ with J′=N′.
AU - Mikhail Lemeshko
AU - Friedrich, Břetislav
ID - 2149
IS - 1
JF - Physical Review A - Atomic, Molecular, and Optical Physics
TI - Collisions of paramagnetic molecules in magnetic fields: An analytic model based on Fraunhofer diffraction of matter waves
VL - 79
ER -
TY - JOUR
AB - We examine the effects of a linearly polarized nonresonant radiative field on the dynamics of rotationally inelastic Na+ + N2 collisions at eV collision energies. Our treatment is based on the Fraunhofer model of matter wave scattering and its recent extension to collisions in electric fields [M. Lemeshko, B. Friedrich, J. Chem. Phys. 129 (2008) 024301]. The nonresonant radiative field changes the effective shape of the target molecule by aligning it in the space-fixed frame. This markedly alters the differential and integral scattering cross-sections. As the cross-sections can be evaluated for a polarization of the radiative field collinear or perpendicular to the relative velocity vector, the model also offers predictions about steric asymmetry of the collisions.
AU - Mikhail Lemeshko
AU - Friedrich, Břetislav
ID - 2150
IS - 1-3
JF - International Journal of Mass Spectrometry
TI - The effect of a nonresonant radiative field on low-energy rotationally inelastic Na+ + N2 collisions
VL - 280
ER -
TY - JOUR
AB - By making use of the quantization rule of Raab and Friedrich [Phys. Rev. A 78, 022707 (2008)], we derive simple and accurate formulae for the number of rotational states supported by a weakly bound vibrational level of a diatomic molecule and the rotational constants of any such levels up to the threshold, and provide a criterion for determining whether a given weakly bound vibrational level is rotationless. The results depend solely on the long-range part of the molecular potential and are applicable to halo molecules.
AU - Mikhail Lemeshko
AU - Friedrich, Břetislav
ID - 2191
IS - 5
JF - Physical Review A - Atomic, Molecular, and Optical Physics
TI - Rotational and rotationless states of weakly bound molecules
VL - 79
ER -
TY - JOUR
AB - We develop an analytic model of thermal state-to-state rotationally inelastic collisions of asymmetric-top molecules with closed-shell atoms in electric fields and apply it to the Ar-H2O collision system. The predicted cross sections as well as the steric asymmetry of the collisions show at fields up to 150 kV/cm characteristic field-dependent features which can be experimentally tested. Particularly suitable candidates for such tests are the 000 → 220 and 101→ 221 channels, arising from the relaxation of the field-free selection rules due to the hybridization of J states by the field. Averaging over the M' product channels is found to largely obliterate the orientation effects brought about by the field.
AU - Mikhail Lemeshko
AU - Friedrich, Břetislav
ID - 2192
IS - 52
JF - Journal of Physical Chemistry A
TI - Model analysis of rotationally inelastic Ar + H2O scattering in an electric field
VL - 113
ER -
TY - JOUR
AB - We show that weakly bound molecules can be probed by "shaking" in a pulsed nonresonant laser field. The field introduces a centrifugal term which expels the highest vibrational level from the potential that binds it. Our numerical simulations applied to the Rb2 and KRb Feshbach molecules indicate that shaking by feasible laser pulses can be used to accurately recover the square of the vibrational wave function and, by inversion, also the long-range part of the molecular potential.
AU - Mikhail Lemeshko
AU - Friedrich, Břetislav
ID - 2193
IS - 5
JF - Physical Review Letters
TI - Probing weakly bound molecules with nonresonant light
VL - 103
ER -
TY - GEN
AB - We consider probabilistic automata on infinite words with acceptance defined by safety, reachability, Büchi, coBüchi and limit-average conditions. We consider quantitative and qualitative decision problems. We present extensions and adaptations of proofs of [GO09] and present a precise characterization of the decidability and undecidability frontier of the quantitative and qualitative decision problems.
AU - Chatterjee, Krishnendu
ID - 5392
SN - 2664-1690
TI - Probabilistic automata on infinite words: Decidability and undecidability results
ER -
TY - GEN
AB - Gist is a tool that (a) solves the qualitative analysis problem of turn-based probabilistic games with ω-regular objectives; and (b) synthesizes reasonable environment assumptions for synthesis of unrealizable specifications. Our tool provides efficient implementations of several reduction based techniques to solve turn-based probabilistic games, and uses the analysis of turn-based probabilistic games for synthesizing environment assumptions for unrealizable specifications.
AU - Chatterjee, Krishnendu
AU - Henzinger, Thomas A
AU - Jobstmann, Barbara
AU - Radhakrishna, Arjun
ID - 5393
SN - 2664-1690
TI - Gist: A solver for probabilistic games
ER -
TY - GEN
AB - We consider two-player games played on graphs with request-response and finitary Streett objectives. We show these games are PSPACE-hard, improving the previous known NP-hardness. We also improve the lower bounds on memory required by the winning strategies for the players.
AU - Chatterjee, Krishnendu
AU - Henzinger, Thomas A
AU - Horn, Florian
ID - 5394
SN - 2664-1690
TI - Improved lower bounds for request-response and finitary Streett games
ER -
TY - GEN
AB - We study observation-based strategies for partially-observable Markov decision processes (POMDPs) with omega-regular objectives. An observation-based strategy relies on partial information about the history of a play, namely, on the past sequence of observa- tions. We consider the qualitative analysis problem: given a POMDP with an omega-regular objective, whether there is an observation-based strategy to achieve the objective with probability 1 (almost-sure winning), or with positive probability (positive winning). Our main results are twofold. First, we present a complete picture of the computational complexity of the qualitative analysis of POMDPs with parity objectives (a canonical form to express omega-regular objectives) and its subclasses. Our contribution consists in establishing several upper and lower bounds that were not known in literature. Second, we present optimal bounds (matching upper and lower bounds) on the memory required by pure and randomized observation-based strategies for the qualitative analysis of POMDPs with parity objectives and its subclasses.
AU - Chatterjee, Krishnendu
AU - Doyen, Laurent
AU - Henzinger, Thomas A
ID - 5395
SN - 2664-1690
TI - Qualitative analysis of partially-observable Markov decision processes
ER -
TY - JOUR
AB - The human CDK8 subcomplex (CDK8, cyclin C, Med12, and Med13) negatively regulates transcription in ways not completely defined; past studies suggested CDK8 kinase activity was required for its repressive function. Using a reconstituted transcription system together with recombinant or endogenous CDK8 subcomplexes, we demonstrate that, in fact, Med12 and Med13 are critical for subcomplex-dependent repression, whereas CDK8 kinase activity is not. A hallmark of activated transcription is efficient reinitiation from promoter-bound scaffold complexes that recruit a series of pol II enzymes to the gene. Notably, the CDK8 submodule strongly represses even reinitiation events, suggesting a means to fine tune transcript levels. Structural and biochemical studies confirm the CDK8 submodule binds the Mediator leg/tail domain via the Med13 subunit, and this submodule-Mediator association precludes pol II recruitment. Collectively, these results reveal the CDK8 subcomplex functions as a simple switch that controls the Mediator-pol II interaction to help regulate transcription initiation and reinitiation events. As Mediator is generally required for expression of protein-coding genes, this may reflect a common mechanism by which activated transcription is shut down in human cells.
AU - Knuesel, Matthew
AU - Meyer, Krista
AU - Bernecky, Carrie A
AU - Taatjes, Dylan
ID - 599
IS - 4
JF - Genes and Development
TI - The human CDK8 subcomplex is a molecular switch that controls Mediator coactivator function
VL - 23
ER -
TY - CHAP
AB - Let g be a cubic polynomial with integer coefficients and n>9 variables, and assume that the congruence g=0 modulo p^k is soluble for all prime powers p^k. We show that the equation g=0 has infinitely many integer solutions when the cubic part of g defines a projective hypersurface with singular locus of dimension <n-10. The proof is based on the Hardy-Littlewood circle method.
AU - Browning, Timothy D
AU - Heath Brown, Roger
ID - 164
T2 - Analytic Number Theory: Essays in honour of Klaus Roth
TI - Integral points on cubic hypersurfaces
ER -
TY - JOUR
AB - One possible way to produce ultra-cold, high-phase-space-density quantum gases of molecules in the rovibronic ground state is given by molecule association from quantum-degenerate atomic gases on a Feshbach resonance and subsequent coherent optical multi-photon transfer into the rovibronic ground state. In ultra-cold samples of Cs2 molecules, we observe two-photon dark resonances that connect the intermediate rovibrational level |v=73,J=2 with the rovibrational ground state |v=0,J=0 of the singlet X 1 ∑ g + ground-state potential. For precise dark resonance spectroscopy we exploit the fact that it is possible to efficiently populate the level |v=73,J=2 by two-photon transfer from the dissociation threshold with the stimulated Raman adiabatic passage (STIRAP) technique. We find that at least one of the two-photon resonances is sufficiently strong to allow future implementation of coherent STIRAP transfer of a molecular quantum gas to the rovibrational ground state |v=0,J=0.
AU - Mark, Manfred
AU - Danzl, Johann G
AU - Haller, Elmar
AU - Gustavsson, Mattias
AU - Bouloufa, Nadia
AU - Dulieu, Olivier
AU - Salami, Houssam
AU - Bergeman, Thomas
AU - Ritsch, Helmut
AU - Hart, Russell
AU - Nägerl, Hanns
ID - 1038
IS - 2
JF - Applied Physics B: Lasers and Optics
TI - Dark resonances for ground-state transfer of molecular quantum gases
VL - 95
ER -
TY - JOUR
AB - Ultracold atomic physics offers myriad possibilities to study strongly correlated many-body systems in lower dimensions. Typically, only ground-state phases are accessible. Using a tunable quantum gas of bosonic cesium atoms, we realized and controlled in one-dimensional geometry a highly excited quantum phase that is stabilized in the presence of attractive interactions by maintaining and strengthening quantum correlations across a confinement-induced resonance. We diagnosed the crossover from repulsive to attractive interactions in terms of the stiffness and energy of the system. Our results open up the experimental study of metastable, excited, many-body phases with strong correlations and their dynamical properties.
AU - Haller, Elmar
AU - Gustavsson, Mattias
AU - Mark, Manfred
AU - Danzl, Johann G
AU - Hart, Russell
AU - Pupillo, Guido
AU - Nägerl, Hanns
ID - 1040
IS - 5945
JF - Science
TI - Realization of an excited, strongly correlated quantum gas Phase
VL - 325
ER -
TY - JOUR
AB - We demonstrate efficient transfer of ultracold molecules into a deeply bound rovibrational level of the singlet ground state potential in the presence of an optical lattice. The overall molecule creation efficiency is 25%, and the transfer efficiency to the rovibrational level |v = 73, J = 2) is above 80%. We find that the molecules in |v = 73, J = 2) are trapped in the optical lattice, and that the lifetime in the lattice is limited by optical excitation by the lattice light. The molecule trapping time for a lattice depth of 15 atomic recoil energies is about 20 ms. We determine the trapping frequency by the lattice phase and amplitude modulation technique. It will now be possible to transfer the molecules to the rovibrational ground state |v = 0, J = 0) in the presence of the optical lattice.
AU - Danzl, Johann G
AU - Mark, Manfred
AU - Haller, Elmar
AU - Gustavsson, Mattias
AU - Hart, Russell
AU - Liem, Andreas
AU - Zellmer, Holger
AU - Nägerl, Hanns
ID - 1041
JF - New Journal of Physics
TI - Deeply bound ultracold molecules in an optical lattice
VL - 11
ER -
TY - JOUR
AB - One possibility for the creation of ultracold, high phase space density quantum gases of molecules in the rovibronic ground state relies on first associating weakly-bound molecules from quantum-degenerate atomic gases on a Feshbach resonance and then transferring the molecules via several steps of coherent two-photon stimulated Raman adiabatic passage (STIRAP) into the rovibronic ground state. Here, in ultracold samples of Cs2 Feshbach molecules produced out of ultracold samples of Cs atoms, we observe several optical transitions to deeply-bound rovibrational levels of the excited 0 u+ molecular potentials with high resolution. At least one of these transitions, although rather weak, allows efficient STIRAP transfer into the deeply-bound vibrational level v = 73> of the singlet X 1Σg+ ground state potential, as recently demonstrated (J. G. Danzl, E. Haller, M. Gustavsson, M. J. Mark, R. Hart, N. Bouloufa, O. Dulieu, H. Ritsch, and H.-C. Nägerl, Science, 2008, 321, 1062). From this level, the rovibrational ground state v = 0, J = 0> can be reached with one more transfer step. In total, our results show that coherent ground state transfer for Cs2 is possible using a maximum of two successive two-photon STIRAP processes or one single four-photon STIRAP process.
AU - Danzl, Johann G
AU - Mark, Manfred
AU - Haller, Elmar
AU - Gustavsson, Mattias
AU - Bouloufa, Nadia
AU - Dulieu, Olivier
AU - Ritsch, Helmut
AU - Hart, Russell
AU - Nägerl, Hanns
ID - 1043
JF - Faraday Discussions
TI - Precision molecular spectroscopy for ground state transfer of molecular quantum gases
VL - 142
ER -
TY - JOUR
AB - As part of an ongoing effort to develop a parameterization of wave-induced abyssal mixing, the authors derive an heuristic model for nonlinear wave breaking and energy dissipation associated with internal tides. Then the saturation and dissipation of internal tides for idealized and observed topography samples are investigated. One of the main results is that the wave-induced mixing could be more intense and more confined to the bottom than previously assumed in numerical models. Furthermore, in this model wave breaking and mixing clearly depend on the small scales of the topography below 10 km or so, which is below the current resolution of global bathymetry. This motivates the use of a statistical approach to represent the unresolved topography when addressing the role of internal tides in mixing the deep ocean.
AU - MULLER, Caroline J
AU - Bühler, Oliver
ID - 9147
IS - 9
JF - Journal of Physical Oceanography
KW - Oceanography
SN - 1520-0485
TI - Saturation of the internal tides and induced mixing in the abyssal ocean
VL - 39
ER -
TY - JOUR
AB - Several observational studies have shown a tight relationship between tropical precipitation and column‐integrated water vapor. We show that the observed relationship in the tropics between column‐integrated water vapor, precipitation, and its variance can be qualitatively reproduced by a simple and physically motivated two‐layer model. It has previously been argued that features of this relationship could be explained by analogy with the theory of continuous phase transitions. Instead, our model explicitly assumes that the onset of precipitation is governed by a stability threshold involving boundary‐layer water vapor. This allows us to explain the precipitation‐humidity relationship over a broader range of water vapor values, and may explain the observed temperature dependence of the relationship.
AU - MULLER, Caroline J
AU - Back, Larissa E.
AU - O'Gorman, Paul A.
AU - Emanuel, Kerry A.
ID - 9148
IS - 16
JF - Geophysical Research Letters
KW - General Earth and Planetary Sciences
KW - Geophysics
SN - 0094-8276
TI - A model for the relationship between tropical precipitation and column water vapor
VL - 36
ER -
TY - GEN
AB - Ising models with pairwise interactions are the least structured, or maximum-entropy, probability distributions that exactly reproduce measured pairwise correlations between spins. Here we use this equivalence to construct Ising models that describe the correlated spiking activity of populations of 40 neurons in the salamander retina responding to natural movies. We show that pairwise interactions between neurons account for observed higher-order correlations, and that for groups of 10 or more neurons pairwise interactions can no longer be regarded as small perturbations in an independent system. We then construct network ensembles that generalize the network instances observed in the experiment, and study their thermodynamic behavior and coding capacity. Based on this construction, we can also create synthetic networks of 120 neurons, and find that with increasing size the networks operate closer to a critical point and start exhibiting collective behaviors reminiscent of spin glasses. We examine closely two such behaviors that could be relevant for neural code: tuning of the network to the critical point to maximize the ability to encode diverse stimuli, and using the metastable states of the Ising Hamiltonian as neural code words.
AU - Gasper Tkacik
AU - Schneidman, Elad
AU - Berry, Michael J
AU - Bialek, William S
ID - 3732
T2 - ArXiv
TI - Spin glass models for a network of real neurons
VL - q-bio.NC
ER -
TY - JOUR
AB - There is a close analogy between statistical thermodynamics and the evolution of allele frequencies under mutation, selection and random drift. Wright's formula for the stationary distribution of allele frequencies is analogous to the Boltzmann distribution in statistical physics. Population size, 2N, plays the role of the inverse temperature, 1/kT, and determines the magnitude of random fluctuations. Log mean fitness, View the MathML source, tends to increase under selection, and is analogous to a (negative) energy; a potential function, U, increases under mutation in a similar way. An entropy, SH, can be defined which measures the deviation from the distribution of allele frequencies expected under random drift alone; the sum View the MathML source gives a free fitness that increases as the population evolves towards its stationary distribution. Usually, we observe the distribution of a few quantitative traits that depend on the frequencies of very many alleles. The mean and variance of such traits are analogous to observable quantities in statistical thermodynamics. Thus, we can define an entropy, SΩ, which measures the volume of allele frequency space that is consistent with the observed trait distribution. The stationary distribution of the traits is View the MathML source; this applies with arbitrary epistasis and dominance. The entropies SΩ, SH are distinct, but converge when there are so many alleles that traits fluctuate close to their expectations. Populations tend to evolve towards states that can be realised in many ways (i.e., large SΩ), which may lead to a substantial drop below the adaptive peak; we illustrate this point with a simple model of genetic redundancy. This analogy with statistical thermodynamics brings together previous ideas in a general framework, and justifies a maximum entropy approximation to the dynamics of quantitative traits.
AU - Barton, Nicholas H
AU - Coe, Jason
ID - 3775
IS - 2
JF - Journal of Theoretical Biology
TI - On the application of statistical physics to evolutionary biology
VL - 259
ER -
TY - JOUR
AB - Why are sinistral snails so rare? Two main hypotheses are that selection acts against the establishment of new coiling morphs, because dextral and sinistral snails have trouble mating, or else a developmental constraint prevents the establishment of sinistrals. We therefore used an isolate of the snail Lymnaea stagnalis, in which sinistrals are rare, and populations of Partula suturalis, in which sinistrals are common, as well as a mathematical model, to understand the circumstances by which new morphs evolve. The main finding is that the sinistral genotype is associated with reduced egg viability in L. stagnalis, but in P. suturalis individuals of sinistral and dextral genotype appear equally fecund, implying a lack of a constraint. As positive frequency-dependent selection against the rare chiral morph in P. suturalis also operates over a narrow range (< 3%), the results suggest a model for chiral evolution in snails in which weak positive frequency-dependent selection may be overcome by a negative frequency-dependent selection, such as reproductive character displacement. In snails, there is not always a developmental constraint. As the direction of cleavage, and thus the directional asymmetry of the entire body, does not generally vary in other Spiralia (annelids, echiurans, vestimentiferans, sipunculids and nemerteans), it remains an open question as to whether this is because of a constraint and/or because most taxa do not have a conspicuous external asymmetry (like a shell) upon which selection can act.
AU - Davison, Angus
AU - Barton, Nicholas H
AU - Clarke, Bryan
ID - 3780
IS - 8
JF - Journal of Evolutionary Biology
TI - The effect of chirality phenotype and genotype on the fecundity and viability of Partula suturalis and Lymnaea stagnalis: Implications for the evolution of sinistral snails
VL - 22
ER -