@article{3867, abstract = {Weighted automata are nondeterministic automata with numerical weights on transitions. They can define quantitative languages L that assign to each word w a real number L(w). In the case of infinite words, the value of a run is naturally computed as the maximum, limsup, liminf, limit-average, or discounted-sum of the transition weights. The value of a word w is the supremum of the values of the runs over w. We study expressiveness and closure questions about these quantitative languages. We first show that the set of words with value greater than a threshold can be omega-regular for deterministic limit-average and discounted-sum automata, while this set is always omega-regular when the threshold is isolated (i.e., some neighborhood around the threshold contains no word). In the latter case, we prove that the omega-regular language is robust against small perturbations of the transition weights. We next consider automata with transition weights 0 or 1 and show that they are as expressive as general weighted automata in the limit-average case, but not in the discounted-sum case. Third, for quantitative languages L-1 and L-2, we consider the operations max(L-1, L-2), min(L-1, L-2), and 1 - L-1, which generalize the boolean operations on languages, as well as the sum L-1 + L-2. We establish the closure properties of all classes of quantitative languages with respect to these four operations.}, author = {Chatterjee, Krishnendu and Doyen, Laurent and Henzinger, Thomas A}, journal = {Logical Methods in Computer Science}, number = {3}, pages = {1 -- 23}, publisher = {International Federation for Computational Logic}, title = {{Expressiveness and closure properties for quantitative languages}}, doi = {10.2168/LMCS-6(3:10)2010}, volume = {6}, year = {2010}, } @article{3868, abstract = {Simulation and bisimulation metrics for stochastic systems provide a quantitative generalization of the classical simulation and bisimulation relations. These metrics capture the similarity of states with respect to quantitative specifications written in the quantitative mu-calculus and related probabilistic logics. We first show that the metrics provide a bound for the difference in long-run average and discounted average behavior across states, indicating that the metrics can be used both in system verification, and in performance evaluation. For turn-based games and MDPs, we provide a polynomial-time algorithm for the computation of the one-step metric distance between states. The algorithm is based on linear programming; it improves on the previous known exponential-time algorithm based on a reduction to the theory of reals. We then present PSPACE algorithms for both the decision problem and the problem of approximating the metric distance between two states, matching the best known algorithms for Markov chains. For the bisimulation kernel of the metric our algorithm works in time O(n(4)) for both turn-based games and MDPs; improving the previously best known O(n(9).log(n)) time algorithm for MDPs. For a concurrent game G, we show that computing the exact distance be tween states is at least as hard as computing the value of concurrent reachability games and the square-root-sum problem in computational geometry. We show that checking whether the metric distance is bounded by a rational r, can be done via a reduction to the theory of real closed fields, involving a formula with three quantifier alternations, yielding O(vertical bar G vertical bar(O(vertical bar G vertical bar 5))) time complexity, improving the previously known reduction, which yielded O(vertical bar G vertical bar(O(vertical bar G vertical bar 7))) time complexity. These algorithms can be iterated to approximate the metrics using binary search}, author = {Chatterjee, Krishnendu and De Alfaro, Luca and Majumdar, Ritankar and Raman, Vishwanath}, journal = {Logical Methods in Computer Science}, number = {3}, pages = {1 -- 27}, publisher = {International Federation for Computational Logic}, title = {{Algorithms for game metrics}}, doi = {10.2168/LMCS-6(3:13)2010}, volume = {6}, year = {2010}, } @article{111, abstract = {Thin streams of liquid commonly break up into characteristic droplet patterns owing to the surface-tension-driven PlateauRayleigh instability 1-3. Very similar patterns are observed when initially uniform streams of dry granular material break up into clusters of grains4-6, even though flows of macroscopic particles are considered to lack surface tension7,8. Recent studies on freely falling granular streams tracked fluctuations in the stream profile9, but the clustering mechanism remained unresolved because the full evolution of the instability could not be observed. Here we demonstrate that the cluster formation is driven by minute, nanoNewton cohesive forces that arise from a combination of van der Waals interactions and capillary bridges between nanometre-scale surface asperities. Our experiments involve high-speed video imaging of the granular stream in the co-moving frame, control over the properties of the grain surfaces and the use of atomic force microscopy to measure grain-grain interactions. The cohesive forces that we measure correspond to an equivalent surface tension five orders of magnitude below that, of ordinary liquids. We find that, the shapes of these weakly cohesive, non-thermal clusters of macroscopic particles closely resemble droplets resulting from thermally induced rupture of liquid nanojets 10-12.}, author = {Royer, John and Evans, Daniel and Oyarte, Loreto and Guo, Qiti and Kapit, Eliot and Möbius, Matthias and Waitukaitis, Scott R and Jaeger, Heinrich}, journal = {Nature}, number = {7250}, pages = {1110 -- 1113}, publisher = {Nature Publishing Group}, title = {{High-speed tracking of rupture and clustering in freely falling granular streams}}, doi = {10.1038/nature08115}, volume = {459}, year = {2009}, } @article{2868, abstract = {Plants exhibit an amazing developmental flexibility. Plant embryogenesis results in the establishment of a simple apical-basal axis represented by apical shoot and basal root meristems. Later, during postembryonic growth, shaping of the plant body continues by the formation and activation of numerous adjacent meristems that give rise to lateral shoot branches, leaves, flowers, or lateral roots. This developmental plasticity reflects an important feature of the plant's life strategy based on the rapid reaction to different environmental stimuli, such as temperature fluctuations, availability of nutrients, light or water and response resulting in modulation of developmental programs. Plant hormones are important endogenous factors for the integration of these environmental inputs and regulation of plant development. After a period of studies focused primarily on single hormonal pathways that enabled us to understand the hormone perception and signal transduction mechanisms, it became obvious that the developmental output mediated by a single hormonal pathway is largely modified through a whole network of interactions with other hormonal pathways. In this review, we will summarize recent knowledge on hormonal networks that regulate the development and growth of root with focus on the hormonal interactions that shape the root apical meristem. }, author = {Eva Benková and Hejátko, Jan}, journal = {Plant Molecular Biology}, number = {4}, pages = {383 -- 396}, publisher = {Springer}, title = {{Hormone interactions at the root apical meristem}}, doi = {10.1007/s11103-008-9393-6}, volume = {69}, year = {2009}, } @article{3048, abstract = {Endocytic vesicle trafficking is crucial for regulating activity and localization of plasma membrane components, but the process is still poorly genetically defined in plants. Membrane proteins of the PIN-FORMED (PIN) family exhibit polar localization in plant cells and facilitate cellular efflux of the plant hormone auxin, thereby regulating multiple developmental processes [1, 2]. PIN proteins undergo constitutive endocytosis and GNOM ARF GEF-dependent recycling [3-5], and their localization is under extensive regulation by developmental and environmental cues [6-9]. We designed a fluorescence imaging-based screen to identify Arabidopsis thaliana mutants defective in internalization of proteins including PINs from the plasma membrane. We identified three mutant loci, BFA-visualized endocytic trafficking defective1 (ben1) through ben3 that do not efficiently accumulate PIN1-GFP in intracellular compartments after inhibition of recycling and secretion by fungal toxin brefeldin A (BFA). Fine mapping revealed that BEN1 encodes an ARF GEF vesicle trafficking regulator from the functionally uncharacterized BIG class. ben1 mutant has been previously implicated in pathogen response [10] and shows cell polarity, BFA sensitivity, and growth defects. BEN1 is involved in endocytosis of plasma membrane proteins and localizes to early endocytic compartments distinct from GNOM-positive endosomes. Our results identify BEN1 as the ARF GEF mediating early endosomal traffic.}, author = {Tanaka, Hirokazu and Kitakura, Saeko and De Rycke, Riet M and De Groodt, Ruth and Jirí Friml}, journal = {Current Biology}, number = {5}, pages = {391 -- 397}, publisher = {Cell Press}, title = {{Fluorescence imaging based screen identifies ARF GEF component of early endosomal trafficking}}, doi = {10.1016/j.cub.2009.01.057}, volume = {19}, year = {2009}, } @article{21513, abstract = {Numerical modelling of the deformation of a polymer using the finite elements method in axisymetrical mode was performed using the LsDyna® software to describe the filling of micro-cavities during the forming process of the material using the hot embossing. These simulations firstly allow verifying whether the chosen forming process conditions promote or not an optimized filling of the superficial cavities in order to achieve precise replicas which best reproduce the superficial topography of the mould. The simulations were carried out to evaluate the filling of the cavities taking into account the mechanical behaviour of the selected polymer into the model. Moreover, these models were developed to verify the effect of the distribution of the mould cavities on their filling. The influence of the mobility of non deformable rigid plates on the filling of the cavities represents an auxiliary variable. In the approach presented, the compression plates are assumed to be parallel and non deformable, whereas the polymer disk follows a rubbery behaviour around a temperature equal to 140°C. Globally the modelling results are satisfactory for they are rather close to the experimental observations conducted. In summary, the effect of the normal stress as also the distribution of micro-cavities at the mould surface seem to prevail in the case of the forming process by hot embossing.}, author = {Sahli, Mohamed and Millot, Christine and Roques-Carmes, Charles and Khan Malek, Chantal}, issn = {1432-1858}, journal = {Microsystem Technologies}, number = {6}, pages = {827--835}, publisher = {Springer Nature}, title = {{Experimental analysis and numerical modelling of the forming process of polypropylene replicas of micro-cavities using hot embossing}}, doi = {10.1007/s00542-009-0813-6}, volume = {15}, year = {2009}, } @inproceedings{18726, abstract = {The high sensitivity of JWST will open a new window on the end of the cosmological dark ages. Small stellar clusters, with a stellar mass of several × 106 M⊙, and low-mass black holes (BHs), with a mass of several $× 105 M⊙ should be directly detectable out to redshift z = 10, and individual supernovae (SNe) and gamma ray burst GRB afterglows are bright enough to be visible beyond this redshift. Dense primordial gas, in the process of collapsing from large scales to form protogalaxies, may also be possible to image through diffuse recombination line emission, possibly even before stars or BHs are formed. In this article, I discuss the key physical processes that are expected to have determined the sizes of the first star–clusters and black holes, and the prospect of studying these objects by direct detections with JWST and with other instruments. The direct light emitted by the very first stellar clusters and intermediate-mass black holes at z > 10 will likely fall below JWST’s detection threshold. However, JWST could reveal a decline at the faint-end of the high-redshift luminosity function, and thereby shed light on radiative and other feedback effects that operate at these early epochs. JWST will also have the sensitivity to detect individual SNe from beyond z = 10. In a dedicated survey lasting for several weeks, thousands of SNe could be detected at z > 6, with a redshift distribution extending to the formation of the very first stars at z ≳ 15. Using these SNe as tracers may be the only method to map out the earliest stages of the cosmic star–formation history. Finally, we point out that studying the earliest objects at high redshift will also offer a new window on the primordial power spectrum, on ∼100 times smaller scales than probed by current large-scale structure data.}, author = {Haiman, Zoltán}, booktitle = {Astrophysics and Space Science Proceedings}, isbn = {9781402094569}, issn = {1570-6605}, pages = {385--418}, publisher = {Springer Nature}, title = {{Observing the first stars and black holes}}, doi = {10.1007/978-1-4020-9457-6_15}, year = {2009}, } @inbook{18735, abstract = {The high sensitivity of JWST will open a new window on the end of the cosmological dark ages. Small stellar clusters, with a stellar mass of several × 106 M⊙, and low-mass black holes (BHs), with a mass of several $× 105 M⊙ should be directly detectable out to redshift z = 10, and individual supernovae (SNe) and gamma ray burst GRB afterglows are bright enough to be visible beyond this redshift. Dense primordial gas, in the process of collapsing from large scales to form protogalaxies, may also be possible to image through diffuse recombination line emission, possibly even before stars or BHs are formed. In this article, I discuss the key physical processes that are expected to have determined the sizes of the first star–clusters and black holes, and the prospect of studying these objects by direct detections with JWST and with other instruments. The direct light emitted by the very first stellar clusters and intermediate-mass black holes at z > 10 will likely fall below JWST’s detection threshold. However, JWST could reveal a decline at the faint-end of the high-redshift luminosity function, and thereby shed light on radiative and other feedback effects that operate at these early epochs. JWST will also have the sensitivity to detect individual SNe from beyond z = 10. In a dedicated survey lasting for several weeks, thousands of SNe could be detected at z > 6, with a redshift distribution extending to the formation of the very first stars at z ≳ 15. Using these SNe as tracers may be the only method to map out the earliest stages of the cosmic star–formation history. Finally, we point out that studying the earliest objects at high redshift will also offer a new window on the primordial power spectrum, on ∼100 times smaller scales than probed by current large-scale structure data.}, author = {Haiman, Zoltán}, booktitle = {Astrophysics in the Next Decade}, editor = {Thronson, Harley A. and Stiavelli, Massimo and Tielens, Alexander}, isbn = {9781402094569}, issn = {1570-6605}, pages = {385--418}, publisher = {Springer Nature}, title = {{Observing the First Stars and Black Holes}}, doi = {10.1007/978-1-4020-9457-6_15}, year = {2009}, } @article{1984, abstract = {In animal and plant cells, mitotic chromatin locally generates microtubules that self-organize into a mitotic spindle, and its dimensions and bipolar symmetry are essential for accurate chromosome segregation. By immobilizing microscopic chromatin-coated beads on slide surfaces using a microprinting technique, we have examined the effect of chromatin on the dimensions and symmetry of spindles in Xenopus laevis cytoplasmic extracts. While circular spots with diameters around 14-18 μm trigger bipolar spindle formation, larger spots generate an incorrect number of poles. We also examined lines of chromatin with various dimensions. Their length determined the number of poles that formed, with a 6 × 18 μm rectangular patch generating normal spindle morphology. Around longer lines, multiple poles formed and the structures were disorganized. While lines thinner than 10 μm generated symmetric structures, thicker lines induced the formation of asymmetric structures where all microtubules are on the same side of the line. Our results show that chromatin defines spindle shape and orientation. For a video summary of this article, see the PaperFlick file available with the online Supplemental Data.}, author = {Dinarina, Ana and Pugieux, Céline and Corral, Maria M and Martin Loose and Spatz, Joachim P and Karsenti, Éric and Nédélec, François J}, journal = {Cell}, number = {3}, pages = {502 -- 513}, publisher = {Cell Press}, title = {{Chromatin shapes the mitotic spindle}}, doi = {10.1016/j.cell.2009.05.027}, volume = {138}, year = {2009}, } @article{17735, abstract = {The supermassive black holes (SMBHs) massive enough to power the bright redshift ~6 quasars observed in the Sloan Digital Sky Survey (SDSS) are thought to have assembled by mergers and/or gas accretion from less massive "seed" BHs. If the seeds are the ~100 Msol remnant BHs from the first generation of stars, they must be in place well before redshift z=6, and must avoid being ejected from their parent proto-galaxies by the large (few hundred km/s) kicks they suffer from gravitational-radiation induced recoil during mergers with other BHs. We simulate the SMBH mass function at redshift z=6 using dark matter (DM) halo merger trees, coupled with a prescription for the halo occupation fraction, accretion histories, and radial recoil trajectories of the growing BHs. Our purpose is (i) to map out plausible scenarios for successful assembly of the z~6 quasar BHs by exploring a wide region of parameter space, and (ii) to predict the rate of low-frequency gravitational wave events detectable by the Laser Interferometer Space Antenna (LISA) for each such scenario. Our main findings are as follows: (1) ~100 Msol seed BHs can grow into the SDSS quasar BHs without super--Eddington accretion, but only if they form in minihalos by z~30 and subsequently accrete ~60% of the time; (2) the scenarios with optimistic assumptions required to explain the SDSS quasar BHs overproduce the mass density in lower--mass (10^5 to 10^7 Msol) SMBHs by a factor of 100-1000, unless seeds stop forming, or accrete at a severely diminished rates or duty cycles (e.g. due to feedback), at z < 20-30. We also present several successful assembly models and their LISA detection rates, including a "maximal" model that gives the highest rate (~30/yr at z~6) without overproducing the total SMBH density.}, author = {Tanaka, Takamitsu and Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {1798--1822}, publisher = {American Astronomical Society}, title = {{The assembly of supermassive black holes at high redshifts}}, doi = {10.1088/0004-637x/696/2/1798}, volume = {696}, year = {2009}, } @inbook{17736, abstract = {We discuss currently available observational constraints on the reionization history of the intergalactic medium (IGM), and the extent to which accreting black holes (BHs) and stars can help account for these observations. We argue, based on the combined statistics of Lyman α and β absorption in quasar spectra, that the IGM contains a significant amount of neutral hydrogen with nH I/nH ≳ 0.1. On the other hand, we argue, based on the lack of a strong evolution in the observed abundance of Lyman α emitting galaxies beyond z ∼ 5.5, that the mean neutral hydrogen fraction cannot exceed nH I/nH ≈ 0.3 at the same redshift. We conclude that the IGM is experiencing rapid ionization at redshift z ∼ 6. We find that quasar BHs, including faint ones that are individually below the detection thresholds of existing optical and X-ray surveys, are unlikely to drive the evolution of the neutral fraction around this epoch, because they would over-produce the present-day soft X-ray background. On the other hand, the seeds of the z ∼ 6 quasar BHs likely appeared at much earlier epochs (z ∼ 20), and produced hard ionizing radiation by accretion. These early BHs are promising candidates to account for the high redshift (z ∼ 15) ionization implied by the recent cosmic microwave anisotropy data from WMAP. Using a model for the growth of BHs by accretion and mergers in a hierarchical cosmology, we suggest that the early growth of quasars must include a super-Eddington growth phase, and that, although not yet optically identified, the FIRST radio survey may have already detected several thousand > 10^8 M⊙ BHs at z > 6. }, author = {Haiman, Zoltán}, booktitle = {Planets to Cosmology. Essential Science in the Final Years of the Hubble Space Telescope}, editor = {Livio, Mario and Casertano, Stefano}, isbn = {9780521847582}, location = {Baltimore, MD, United States}, pages = {157--173}, publisher = {Cambridge University Press}, title = {{Probing the reionization history of the Universe}}, doi = {10.1017/cbo9780511536328.014}, volume = {18}, year = {2009}, } @article{17769, abstract = {Arguably the best hope of understanding the tail end of the re-ionization of the intergalactic medium (IGM) at redshift z > 6 is through the detection and characterization of the Gunn–Peterson damping wing absorption of the IGM in bright quasar spectra. However, the use of quasar spectra to measure the IGM damping wing requires a model of the quasar's intrinsic Lyman α emission line. Here we quantify the uncertainties in the intrinsic line shapes, and how those uncertainties affect the determination of the IGM neutral fraction. We have assembled a catalogue of high-resolution Hubble Space Telescope spectra of the emission lines of unobscured low-redshift quasars, and have characterized the variance in the shapes of their lines. We then add simulated absorption from the high-redshift IGM to these quasar spectra in order to determine the corresponding uncertainties in re-ionization constraints using current and future samples of z > 6 quasar spectra. We find that, if the redshift of the Lyman α emission line is presumed to coincide with the systemic redshift determined from metal lines, the inferred IGM neutral fraction is systematically biased to low values due to a systematic blueshift of the Lyman α line relative to the metal lines. If a similar blueshift persists in quasars at z > 6, this bias strengthens previous claims of a significant neutral hydrogen fraction at z≈ 6. The bias can be reduced by including a Lyman α blueshift in the modelling procedure, or by excising wavelengths near the Lyman α line centre from the modelling. Intrinsic Lyman α line shape variations still induce significant scatter in the inferred xIGM values. Nevertheless, this scatter still allows a robust distinction between a highly ionized (xIGM∼ 10−3) and a neutral (xIGM= 1) IGM with even a few bright quasars. We conclude that if the variations of the intrinsic Lyman α emission line shapes in high-z quasars are similar to those at low-z, this variation will not limit the usefulness of quasar spectra in probing re-ionization.}, author = {Kramer, R. H. and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {1493--1511}, publisher = {Oxford University Press}, title = {{Probing re-ionization with quasar spectra: The impact of the intrinsic Lyman α emission line shape uncertainty}}, doi = {10.1111/j.1365-2966.2009.15552.x}, volume = {400}, year = {2009}, } @article{17772, abstract = {We utilize the local velocity dispersion function (VDF) of spheroids, together with their inferred age distributions, to predict the VDF at higher redshifts (0 < z lsim 6), under the assumption that (1) most of the stars in each nearby spheroid formed in a single episode and, (2) the velocity dispersion σ remained nearly constant afterward. We assume further that a supermassive BH forms concurrently with the stars, and within ±1 Gyr of the formation of the potential well of the spheroid, and that the relation between the mass of the BH and host velocity dispersion maintains the form M BH vprop σβ with β ≈ 4, but with the normalization allowed to evolve with redshift as vprop(1 + z)α. We compute the BH mass function associated with the VDF at each redshift, and compare the accumulated total BH mass density with that inferred from the integrated quasar luminosity function (LF; the so-called Sołtan argument). This comparison is insensitive to the assumed duty cycle or Eddington ratio of quasar activity, and we find that the match between the two BH mass densities favors a relatively mild redshift evolution, with α ~ 0.33, with a positive evolution as strong as α gsim 1.3 excluded at more than 99% confidence level. A direct match between the characteristic BH mass in the VDF-based and quasar LF-based BH mass functions also yields a mean Eddington ratio of λ ~ 0.5-1 that is roughly constant within 0 lsim z lsim 3. A strong positive evolution in the M BH-σ relation is still allowed by the data if galaxies increase, on average, their velocity dispersions since the moment of formation due to dissipative processes. If we assume that the mean velocity dispersion of the host galaxies evolves as σ(z) = σ(0) × (1 + z)-γ, we find a lower limit of γ gsim 0.23 for α gsim 1.5. The latter estimate represents an interesting constraint for galaxy evolution models and can be tested through hydro simulations. This dissipative model, however, also implies a decreasing λ at higher z, at variance with several independent studies.}, author = {Shankar, Francesco and Bernardi, Mariangela and Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {867--878}, publisher = {American Astronomical Society}, title = {{The evolution of the mbh-σ relation inferred from the age distribution of local early-type galaxies and active galactic nuclei evolution}}, doi = {10.1088/0004-637x/694/2/867}, volume = {694}, year = {2009}, } @article{17797, abstract = {It is well known that an initial population of seed black holes (BHs), formed in the nuclei of low-mass galaxies at high redshift, can simultaneously explain, through their subsequent growth by mergers and accretion, both the observed evolution of the quasar luminosity function (LF) and the distribution of remnant supermassive black hole (SMBH) masses measured in local galactic nuclei. Here we consider three very different initial conditions for this scenario: models in which initial seed BHs form in either all, or only a small fraction (fbh = 0.1 or 0.01) of high-redshift dark matter halos (with Mhalo = 5 × 109 M☉ at z = 6–10). We show that with a suitable and relatively minor adjustment of two global physical parameters (the radiative efficiency and mass accretion time-scale of quasar episodes), models with fbh ≈ 0.1 and 1 can accurately reproduce the observed quasar LF at redshifts 0 < z ≲ 6, as well as the remnant SMBH mass function at z = 0. However, SMBHs remain rare, and the normalization of the high-z quasar LF and the local SMBH mass function are both significantly underpredicted, if fbh ≲ 0.01. We also show that the merger history of SMBHs, in the mass range detectable by the future Laser Interferometer Space Antenna (LISA) instrument, generically looks different as fbh is varied; this should allow LISA to deliver useful constraints on otherwise degenerate models.}, author = {Lippai, Zoltán and Frei, Zsolt and Haiman, Zoltán}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {1}, pages = {360--368}, publisher = {American Astronomical Society}, title = {{On the occupation fraction of seed black holes in high-redshift dark matter halos}}, doi = {10.1088/0004-637x/701/1/360}, volume = {701}, year = {2009}, } @article{17809, abstract = {Supermassive black hole binaries (SMBHBs) in galactic nuclei are thought to be a common by-product of major galaxy mergers. We use simple disk models for the circumbinary gas and for the binary–disk interaction to follow the orbital decay of SMBHBs with a range of total masses (M) and mass ratios (q), through physically distinct regions of the disk, until gravitational waves (GWs) take over their evolution. Prior to the GW-driven phase, the viscous decay is generically in the stalled "secondary-dominated" regime. SMBHBs spend a non-negligible fraction of a fiducial time of 107 yr at orbital periods between days ≲torb≲ yr, and we argue that they may be sufficiently common to be detectable, provided they are luminous during these stages. A dedicated optical or X-ray survey could identify coalescing SMBHBs statistically, as a population of periodically variable quasars, whose abundance obeys the scaling Nvar ∝ tαvar within a range of periods around tvar∼ tens of weeks. SMBHBs with M ≲ 107 M☉, with 0.5 ≲ α ≲ 1.5, would probe the physics of viscous orbital decay, whereas the detection of a population of higher-mass binaries, with α = 8/3, would confirm that their decay is driven by GWs. The lowest-mass SMBHBs (M ≲ 105–6 M☉) enter the GW-driven regime at short orbital periods, when they are already in the frequency band of the Laser Interferometric Space Antenna (LISA). While viscous processes are negligible in the last few years of coalescence, they could reduce the amplitude of any unresolved background due to near-stationary LISA sources. We discuss modest constraints on the SMBHB population already available from existing data, and the sensitivity and sky coverage requirements for a detection in future surveys. SMBHBs may also be identified from velocity shifts in their spectra; we discuss the expected abundance of SMBHBs as a function of their orbital velocity.}, author = {Haiman, Zoltán and Kocsis, Bence and Menou, Kristen}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {1952--1969}, publisher = {American Astronomical Society}, title = {{The population of viscosity- and gravitational wave-driven supermassive black hole binaries among luminous active galactic nuclei}}, doi = {10.1088/0004-637x/700/2/1952}, volume = {700}, year = {2009}, } @article{2379, author = {Frank, Rupert L and Lieb, Élliott H and Robert Seiringer}, journal = {Journal of the American Mathematical Society}, number = {4}, pages = {925 -- 950}, publisher = {American Mathematical Society}, title = {{Hardy-Lieb-Thirring inequalities for fractional Schrödinger operators}}, doi = {10.1090/S0894-0347-07-00582-6}, volume = {21}, year = {2008}, } @article{2382, abstract = {We show that the Lieb-Liniger model for one-dimensional bosons with repulsive δ-function interaction can be rigorously derived via a scaling limit from a dilute three-dimensional Bose gas with arbitrary repulsive interaction potential of finite scattering length. For this purpose, we prove bounds on both the eigenvalues and corresponding eigenfunctions of three-dimensional bosons in strongly elongated traps and relate them to the corresponding quantities in the Lieb-Liniger model. In particular, if both the scattering length a and the radius r of the cylindrical trap go to zero, the Lieb-Liniger model with coupling constant g ∼ a/r 2 is derived. Our bounds are uniform in g in the whole parameter range 0 ≤ g ≤ ∞, and apply to the Hamiltonian for three-dimensional bosons in a spectral window of size ∼ r -2 above the ground state energy.}, author = {Robert Seiringer and Yin, Jun}, journal = {Communications in Mathematical Physics}, number = {2}, pages = {459 -- 479}, publisher = {Springer}, title = {{The Lieb-Liniger model as a limit of dilute bosons in three dimensions}}, doi = {10.1007/s00220-008-0521-6}, volume = {284}, year = {2008}, } @article{1719, abstract = {We study the mechanics of tissue growth via cell division and cell death (apoptosis). The rearrangements of cells can on large scales and times be captured by a continuum theory which describes the tissue as an effective viscous material with active stresses generated by cell division. We study the effects of anisotropies of cell division on cell rearrangements and show that average cellular trajectories exhibit anisotropic scaling behaviors. If cell division and apoptosis balance, there is no net growth, but for anisotropic cell division the tissue undergoes spontaneous shear deformations. Our description is relevant for the study of developing tissues such as the imaginal disks of the fruit fly Drosophila melanogaster, which grow anisotropically.}, author = {Bittig, Thomas and Wartlick, Ortrud and Anna Kicheva and González-Gaitárr, Marcos and Julicher, Frank}, journal = {New Journal of Physics}, publisher = {IOP Publishing Ltd.}, title = {{Dynamics of anisotropic tissue growth}}, doi = {10.1088/1367-2630/10/6/063001}, volume = {10}, year = {2008}, } @article{3544, abstract = {In the subthalamic nucleus (STN) of Parkinson's disease (PD) patients, a pronounced synchronization of oscillatory activity at beta frequencies (15-30 Hz) accompanies movement difficulties. Abnormal beta oscillations and motor symptoms are concomitantly and acutely suppressed by dopaminergic therapies, suggesting that these inappropriate rhythms might also emerge acutely from disrupted dopamine transmission. The neural basis of these abnormal beta oscillations is unclear, and how they might compromise information processing, or how they arise, is unknown. Using a 6-hydroxydopamine-lesioned rodent model of PD, we demonstrate that beta oscillations are inappropriately exaggerated, compared with controls, in a brain-state-dependent manner after chronic dopamine loss. Exaggerated beta oscillations are expressed at the levels of single neurons and small neuronal ensembles, and are focally present and spatially distributed within STN. They are also expressed in synchronous population activities, as evinced by oscillatory local field potentials, in STN and cortex. Excessively synchronized beta oscillations reduce the information coding capacity of STN neuronal ensembles, which may contribute to parkinsonian motor impairment. Acute disruption of dopamine transmission in control animals with antagonists of D-1/D-2 receptors did not exaggerate STN or cortical beta oscillations. Moreover, beta oscillations were not exaggerated until several days after 6-hydroxydopamine injections. Thus, contrary to predictions, abnormally amplified beta oscillations in cortico-STN circuits do not result simply from an acute absence of dopamine receptor stimulation, but are instead delayed sequelae of chronic dopamine depletion. Targeting the plastic processes underlying the delayed emergence of pathological beta oscillations after continuing dopaminergic dysfunction may offer considerable therapeutic promise.}, author = {Mallet, Nicolas and Pogosyan, Alek and Sharott, Andrew and Csicsvari, Jozsef L and Bolam, John and Brown, Peter and Magill, Peter}, journal = {Journal of Neuroscience}, number = {18}, pages = {4795 -- 4806}, publisher = {Society for Neuroscience}, title = {{Disrupted dopamine transmission and the emergence of exaggerated beta oscillations in subthalamic nucleus and cerebral cortex}}, doi = {10.1523/JNEUROSCI.0123-08.2008}, volume = {28}, year = {2008}, } @article{3826, abstract = {Gamma frequency (30-100 Hz) oscillations in the mature cortex underlie higher cognitive functions. Fast signaling in GABAergic interneuron networks plays a key role in the generation of these oscillations. During development of the rodent brain, gamma activity appears at the end of the first postnatal week, but frequency and synchrony reach adult levels only by the fourth week. However, the mechanisms underlying the maturation of gamma activity are unclear. Here we demonstrate that hippocampal basket cells (BCs), the proposed cellular substrate of gamma oscillations, undergo marked changes in their morphological, intrinsic, and synaptic properties between postnatal day 6 (P6) and P25. During maturation, action potential duration, propagation time, duration of the release period, and decay time constant of IPSCs decreases by approximately 30-60%. Thus, postnatal development converts BCs from slow into fast signaling devices. Computational analysis reveals that BC networks with young intrinsic and synaptic properties as well as reduced connectivity generate oscillations with moderate coherence in the lower gamma frequency range. In contrast, BC networks with mature properties and increased connectivity generate highly coherent activity in the upper gamma frequency band. Thus, late postnatal maturation of BCs enhances coherence in neuronal networks and will thereby contribute to the development of cognitive brain functions.}, author = {Doischer, Daniel and Hosp, Jonas and Yanagawa, Yuchio and Obata, Kunihiko and Jonas, Peter M and Vida, Imre and Bartos, Marlene}, issn = {1529-2401}, journal = {The Journal of Neuroscience}, number = {48}, pages = {12956 -- 68}, publisher = {Society for Neuroscience}, title = {{Postnatal differentiation of basket cells from slow to fast signaling devices}}, doi = {10.1523/JNEUROSCI.2890-08.2008}, volume = {28}, year = {2008}, }