@article{1758, abstract = {We studied the low-energy states of spin-1/2 quantum dots defined in InAs/InP nanowires and coupled to aluminum superconducting leads. By varying the superconducting gap Δ with a magnetic field B we investigated the transition from strong coupling Δ≪T K to weak-coupling Δ≫T K, where T K is the Kondo temperature. Below the critical field, we observe a persisting zero-bias Kondo resonance that vanishes only for low B or higher temperatures, leaving the room to more robust subgap structures at bias voltages between Δ and 2Δ. For strong and approximately symmetric tunnel couplings, a Josephson supercurrent is observed in addition to the Kondo peak. We ascribe the coexistence of a Kondo resonance and a superconducting gap to a significant density of intragap quasiparticle states, and the finite-bias subgap structures to tunneling through Shiba states. Our results, supported by numerical calculations, own relevance also in relation to tunnel-spectroscopy experiments aiming at the observation of Majorana fermions in hybrid nanostructures.}, author = {Lee, Eduardo J and Jiang, Xiaocheng and Aguado, Ramón and Georgios Katsaros and Lieber, Charles M and De Franceschi, Silvano}, journal = {Physical Review Letters}, number = {18}, publisher = {American Physical Society}, title = {{Zero-bias anomaly in a nanowire quantum dot coupled to superconductors}}, doi = {10.1103/PhysRevLett.109.186802}, volume = {109}, year = {2012}, } @article{17613, abstract = {We study the interaction of a supermassive black hole (SMBH) binary and a standard radiatively efficient thin accretion disk. We examine steady-state configurations of the disk and migrating SMBH system, self-consistently accounting for tidal and viscous torques and heating, radiative diffusion limited cooling, gas and radiation pressure, and the decay of the binary's orbit. We obtain a "phase diagram" of the system as a function of binary parameters, showing regimes in which both the disk structure and migration have a different character. Although massive binaries can create a central gap in the disk at large radii, the tidal barrier of the secondary causes a significant pile-up of gas outside of its orbit, which can lead to the closing of the gap. We find that this spillover occurs at an orbital separation as large as ~200 M_7^{-1/2} gravitational radii, where M = 10^7 M_7 Msun is the total binary mass. If the secondary is less massive than ~10^6 Msun, then the gap is closed before gravitational waves (GWs) start dominating the orbital decay. In this regime, the disk is still strongly perturbed, but the piled-up gas continuously overflows as in a porous dam, and crosses inside the secondary's orbit. The corresponding migration rate, which we label Type 1.5, is slower than the usual limiting cases known as Type I and II migration. Compared to an unperturbed disk, the steady-state disk in the overflowing regime is up to several hundred times brighter in the optical bands. Surveys such as PanSTARRS or LSST may discover the periodic variability of this population of binaries. Our results imply that the circumbinary disks around SMBHs can extend to small radii during the last stages of their merger, when they are detectable by LISA, and may produce coincident electromagnetic (EM) emission similar to active galactic nuclei (AGN).}, author = {Kocsis, Bence and Haiman, Zoltán and Loeb, Abraham}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {2680--2700}, publisher = {Oxford University Press}, title = {{Gas pile-up, gap overflow and Type 1.5 migration in circumbinary discs: Application to supermassive black hole binaries}}, doi = {10.1111/j.1365-2966.2012.22118.x}, volume = {427}, year = {2012}, } @article{17636, abstract = {It is commonly believed that the earliest stages of star formation in the Universe were self-regulated by global radiation backgrounds - either by the ultraviolet (UV) Lyman-Werner (LW) photons emitted by the first stars (directly photodissociating H2), or by the X-rays produced by accretion on to the black hole (BH) remnants of these stars (heating the gas but catalysing H2 formation). Recent studies have suggested that a significant fraction of the first stars may have had low masses (a few M⊙). Such stars do not leave BH remnants and they have softer spectra, with copious infrared (IR) radiation at photon energies ∼1 eV. Similar to LW and X-ray photons, these photons have a mean-free path comparable to the Hubble distance, building up an early IR background. Here we show that if soft-spectrum stars, with masses of a few M⊙, contributed ≳0.3 per cent of the UV background (or their mass fraction exceeded ∼80 per cent), then their IR radiation dominated radiative feedback in the early Universe. The feedback is different from the UV feedback from high-mass stars, and occurs through the photodetachment of H− ions, necessary for efficient H2 formation. Nevertheless, we find that the baryon fraction which must be incorporated into low-mass stars in order to suppress H2 cooling is only a factor of a few higher than for high-mass stars.}, author = {Wolcott-Green, J. and Haiman, Zoltán}, issn = {1745-3925}, journal = {Monthly Notices of the Royal Astronomical Society: Letters}, number = {1}, pages = {L51--L55}, publisher = {Oxford University Press}, title = {{Feedback from the infrared background in the early universe}}, doi = {10.1111/j.1745-3933.2012.01298.x}, volume = {425}, year = {2012}, } @inproceedings{17651, abstract = {A decade after their first discovery, the origin of giant supermassive black holes (SMBHs), with masses in excess of 109 Msolar, at redshifts as early as z > 6, remains a puzzle. One possibility is that stellar-mass ``seed'' BHs, left behind by the first stars, accrete gas at close to the Eddington limit during a large fraction (>~ 50%) of the time. While maintaining such a high accretion rate may itself be difficult, here we focus on another, less commonly discussed problem in this scenario: unless BH seed formation and growth are preferentially suppressed in less massive protogalaxies, the mass density in M~106Msolar SMBHs at z ~ 6 already exceeds the locally observed SMBH mass density by several orders of magnitude. We show that the X-rays from the earliest accreting BHs themselves can cause a self-regulation, by partially ionizing and heating the intergalactic medium (IGM). This ``global warming'' suppresses the formation and growth of subsequent generations of BHs in low-mass halos, and can produce excellent agreement with recent estimates of the z = 6 SMBH mass function, without impeding the growth of the largest (M>~109Msolar) holes, which reside in the most massive galaxies that formed first. The proposed gravitational-wave observatory eLISA could detect several tens of major mergers between SMBHs at z > 6.}, author = {Haiman, Zoltán and Tanaka, Takamitsu and Perna, Rosalba}, booktitle = {AIP Conference Proceedings}, issn = {0094-243X}, location = {Kyoto, Japan}, pages = {303--308}, publisher = {American Institute of Physics}, title = {{Self-regulating the early growth of black holes through global warming}}, doi = {10.1063/1.4754372}, volume = {1480}, year = {2012}, } @article{17660, abstract = {Many astrophysical binaries, from planets to black holes, exert strong torques on their circumbinary accretion discs, and are expected to significantly modify the disc structure. Despite the several decade long history of the subject, the joint evolution of the binary + disc system has not been modelled with self-consistent assumptions for arbitrary mass ratios and accretion rates. Here, we solve the coupled binary–disc evolution equations analytically in the strongly perturbed limit, treating the azimuthally averaged angular momentum exchange between the disc and the binary and the modifications to the density, scaleheight, and viscosity self-consistently, including viscous and tidal heating, diffusion limited cooling, radiation pressure and the orbital decay of the binary. We find a solution with a central cavity and a migration rate similar to those previously obtained for Type II migration, applicable for large masses and binary separations, and near-equal mass ratios. However, we identify a distinct new regime, applicable at smaller separations and masses, and mass ratio in the range 10−3 ≲ q ≲ 0.1. For these systems, gas piles up outside the binary's orbit, but rather than creating a cavity, it continuously overflows as in a porous dam. The disc profile is intermediate between a weakly perturbed disc (producing Type I migration) and a disc with a gap (with Type II migration). However, the migration rate of the secondary is typically slower than both Type I and Type II rates. We term this new regime ‘Type 1.5’ migration.}, author = {Kocsis, Bence and Haiman, Zoltán and Loeb, Abraham}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {2660--2679}, publisher = {Oxford University Press}, title = {{Gas pile-up, gap overflow and Type 1.5 migration in circumbinary discs: General theory}}, doi = {10.1111/j.1365-2966.2012.22129.x}, volume = {427}, year = {2012}, } @article{17674, abstract = {The power spectrum of cosmic infrared background (CIB) anisotropies is sensitive to the connection between star formation and dark matter haloes over the entire cosmic star formation history. Here we develop a model that associates star‐forming galaxies with dark matter haloes and their subhaloes. The model is based on a parametrized relation between the dust‐processed infrared luminosity and (sub)halo mass. By adjusting three free parameters, we attempt to simultaneously fit the four frequency bands of the Planck measurement of the CIB anisotropy power spectrum. To fit the data, we find that the star formation efficiency must peak on a halo mass scale of ≈5 × 10^12 M⊙ and the infrared luminosity per unit mass must increase rapidly with redshift. By comparing our predictions with a well‐calibrated phenomenological model for shot noise, and with a direct observation of source counts, we show that the mean duty cycle of the underlying infrared sources must be near unity, indicating that the CIB is dominated by long‐lived quiescent star formation, rather than intermittent short ‘starbursts’. Despite the improved flexibility of our model, the best simultaneous fit to all four Planck channels remains relatively poor. We discuss possible further extensions to alleviate the remaining tension with the data. Our model presents a theoretical framework for a future joint analysis of both background anisotropy and source count measurements.}, author = {Shang, Cien and Haiman, Zoltán and Knox, Lloyd and Oh, S. Peng}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, pages = {2832--2845}, publisher = {Oxford University Press}, title = {{Improved models for cosmic infrared background anisotropies: New constraints on the infrared galaxy population}}, doi = {10.1111/j.1365-2966.2012.20510.x}, volume = {421}, year = {2012}, } @article{17675, abstract = {In this paper, we show that Minkowski Functionals (MFs) of weak gravitational lensing (WL) convergence maps contain significant non-Gaussian, cosmology-dependent information. To do this, we use a large suite of cosmological ray-tracing N-body simulations to create mock WL convergence maps, and study the cosmological information content of MFs derived from these maps. Our suite consists of 80 independent 512^3 N-body runs, covering seven different cosmologies, varying three cosmological parameters Omega_m, w, and sigma_8 one at a time, around a fiducial LambdaCDM model. In each cosmology, we use ray-tracing to create a thousand pseudo-independent 12 deg^2 convergence maps, and use these in a Monte Carlo procedure to estimate the joint confidence contours on the above three parameters. We include redshift tomography at three different source redshifts z_s=1, 1.5, 2, explore five different smoothing scales theta_G=1, 2, 3, 5, 10 arcmin, and explicitly compare and combine the MFs with the WL power spectrum. We find that the MFs capture a substantial amount of information from non-Gaussian features of convergence maps, i.e. beyond the power spectrum. The MFs are particularly well suited to break degeneracies and to constrain the dark energy equation of state parameter w (by a factor of ~ three better than from the power spectrum alone). The non-Gaussian information derives partly from the one-point function of the convergence (through V_0, the "area" MF), and partly through non-linear spatial information (through combining different smoothing scales for V_0, and through V_1 and V_2, the boundary length and genus MFs, respectively). In contrast to the power spectrum, the best constraints from the MFs are obtained only when multiple smoothing scales are combined.}, author = {Kratochvil, Jan M. and Lim, Eugene A. and Wang, Sheng and Haiman, Zoltán and May, Morgan and Huffenberger, Kevin}, issn = {1550-7998}, journal = {Physical Review D}, number = {10}, publisher = {American Physical Society}, title = {{Probing cosmology with weak lensing Minkowski functionals}}, doi = {10.1103/physrevd.85.103513}, volume = {85}, year = {2012}, } @article{17678, abstract = {The spectra of several high-redshift (z>6) quasars have shown evidence for a Gunn-Peterson (GP) damping wing, indicating a substantial mean neutral hydrogen fraction (x_HI > 0.03) in the z ~ 6 intergalactic medium (IGM). However, previous analyses assumed that the IGM was uniformly ionized outside of the quasar's HII region. Here we relax this assumption and model patchy reionization scenarios for a range of IGM and quasar parameters. We quantify the impact of these differences on the inferred x_HI, by fitting the spectra of three quasars: SDSS J1148+5251 (z=6.419), J1030+0524 (z=6.308), and J1623+3112 (z=6.247). We find that the best-fit values of x_HI in the patchy models agree well with the uniform case. More importantly, we confirm that the observed spectra favor the presence of a GP damping wing, with peak likelihoods decreasing by factors of > few - 10 when the spectra are modeled without a damping wing. We also find that the Ly alpha absorption spectra, by themselves, cannot distinguish the damping wing in a relatively neutral IGM from a damping wing in a highly ionized IGM, caused either by an isolated neutral patch, or by a damped Ly alpha absorber (DLA). However, neutral patches in a highly ionized universe (x_HI < 0.01), and DLAs with the large required column densities (N_HI > few x 10^{20} cm^{-2}) are both rare. As a result, when we include reasonable prior probabilities for the line of sight (LOS) to intercept either a neutral patch or a DLA at the required distance of ~ 40-60 comoving Mpc away from the quasar, we find strong lower limits on the neutral fraction in the IGM, x_HI > 0.1 (at 95% confidence). This strengthens earlier claims that a substantial global fraction of hydrogen in the z~6 IGM is in neutral form.}, author = {Schroeder, Joshua and Mesinger, Andrei and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, pages = {3058--3071}, publisher = {Oxford University Press}, title = {{Evidence of Gunn–Peterson damping wings in high-z quasar spectra: Strengthening the case for incomplete reionization at z ∼ 6–7}}, doi = {10.1093/mnras/sts253}, volume = {428}, year = {2012}, } @article{17688, abstract = {Pulsar timing arrays (PTAs) are expected to detect gravitational waves (GWs) from individual low-redshift (z<1.5) compact supermassive (M>10^9 Msun) black hole (SMBH) binaries with orbital periods of approx. 0.1 - 10 yrs. Identifying the electromagnetic (EM) counterparts of these sources would provide confirmation of putative direct detections of GWs, present a rare opportunity to study the environments of compact SMBH binaries, and could enable the use of these sources as standard sirens for cosmology. Here we consider the feasibility of such an EM identification. We show that because the host galaxies of resolved PTA sources are expected to be exceptionally massive and rare, it should be possible to find unique hosts of resolved sources out to redshift z=0.2. At higher redshifts, the PTA error boxes are larger, and may contain as many as 100 massive-galaxy interlopers. The number of candidates, however, remains tractable for follow-up searches in upcoming wide-field EM surveys. We develop a toy model to characterize the dynamics and the thermal emission from a geometrically thin, gaseous disc accreting onto a PTA-source SMBH binary. Our model predicts that at optical and infrared frequencies, the source should appear similar to a typical luminous active galactic nucleus (AGN). However, owing to the evacuation of the accretion flow by the binary's tidal torques, the source might have an unusually low soft X-ray luminosity and weak UV and broad optical emission lines, as compared to an AGN powered by a single SMBH with the same total mass. For sources near z=1, the decrement in the rest-frame UV should be observable as an extremely red optical color. These properties would make the PTA sources stand out among optically luminous AGN, and could allow their unique identification.}, author = {Tanaka, Takamitsu and Menou, Kristen and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, pages = {705--719}, publisher = {Oxford University Press}, title = {{Electromagnetic counterparts of supermassive black hole binaries resolved by pulsar timing arrays}}, doi = {10.1111/j.1365-2966.2011.20083.x}, volume = {420}, year = {2012}, } @article{17705, abstract = {Observations of high-redshift quasars at z>6 imply that supermassive black holes (SMBHs) with masses over a billion solar masses were in place less than 1 Gyr after the Big Bang. If these SMBHs assembled from "seed" BHs left behind by the first stars, then they must have accreted gas at close to the Eddington limit during a large fraction (>50%) of the time. A generic problem with this scenario, however, is that the mass density in million-solar-mass SMBHs at z=6 already exceeds the locally observed SMBH mass density by several orders of magnitude; in order to avoid this overproduction, BH seed formation and growth must become significantly less efficient in less massive protogalaxies, while proceeding uninterrupted in the most massive galaxies that formed first. Using Monte-Carlo realizations of the merger and growth history of BHs, we show that X-rays from the earliest accreting BHs can provide such a feedback mechanism. Our calculations paint a self-consistent picture of black-hole-made climate change, in which the first miniquasars---among them the ancestors of the z>6 quasar SMBHs---globally warm the IGM and suppress the formation and growth of subsequent generations of BHs. We present two specific models with global miniquasar feedback that provide excellent agreement with recent estimates of the z=6 SMBH mass function. For each of these models, we estimate the rate of BH mergers at z>6 that could be detected by the proposed gravitational-wave observatory eLISA/NGO.}, author = {Tanaka, Takamitsu and Perna, Rosalba and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, pages = {2974--2987}, publisher = {Oxford University Press}, title = {{X-ray emission from high-redshift miniquasars: Self-regulating the population of massive black holes through global warming}}, doi = {10.1111/j.1365-2966.2012.21539.x}, volume = {425}, year = {2012}, } @article{767, abstract = {Synchronous distributed algorithms are easier to design and prove correct than algorithms that tolerate asynchrony. Yet, in the real world, networks experience asynchrony and other timing anomalies. In this paper, we address the question of how to efficiently transform an algorithm that relies on synchronous timing into an algorithm that tolerates asynchronous executions. We introduce a transformation technique from synchronous algorithms to indulgent algorithms (Guerraoui, in PODC, pp. 289-297, 2000), which induces only a constant overhead in terms of time complexity in well-behaved executions. Our technique is based on a new abstraction we call an asynchrony detector, which the participating processes implement collectively. The resulting transformation works for the class of colorless distributed tasks, including consensus and set agreement. Interestingly, we also show that our technique is relevant for colored tasks, by applying it to the renaming problem, to obtain the first indulgent renaming algorithm.}, author = {Alistarh, Dan-Adrian and Gilbert, Seth and Guerraoui, Rachid and Travers, Corentin}, journal = {Theory of Computing Systems}, number = {4}, pages = {404 -- 424}, publisher = {Elsevier}, title = {{Generating Fast Indulgent Algorithms}}, doi = {10.1007/s00224-012-9407-2}, volume = {51}, year = {2012}, } @article{7748, abstract = {Female mate choice acts as an important evolutionary force, yet the influence of the environment on both its expression and the selective pressures acting upon it remains unknown. We found consistent heritable differences between females in their choice of mate based on ornament size during a 25‐year study of a population of collared flycatchers. However, the fitness consequences of mate choice were dependent on environmental conditions experienced whilst breeding. Females breeding with highly ornamented males experienced high relative fitness during dry summer conditions, but low relative fitness during wetter years. Our results imply that sexual selection within a population can be highly variable and dependent upon the prevailing weather conditions experienced by individuals.}, author = {Robinson, Matthew Richard and Sander van Doorn, G. and Gustafsson, Lars and Qvarnström, Anna}, issn = {1461-023X}, journal = {Ecology Letters}, number = {6}, pages = {611--618}, publisher = {Wiley}, title = {{Environment-dependent selection on mate choice in a natural population of birds}}, doi = {10.1111/j.1461-0248.2012.01780.x}, volume = {15}, year = {2012}, } @article{7749, abstract = {Although studies on laboratory species and natural populations of vertebrates have shown reproduction to impair later performance, little is known of the age‐specific associations between reproduction and survival, and how such findings apply to the ageing of large, long‐lived species. Herein we develop a framework to examine population‐level patterns of reproduction and survival across lifespan in long‐lived organisms, and decompose those changes into individual‐level effects, and the effects of age‐specific trade‐offs between fitness components. We apply this to an extensive longitudinal dataset on female semi‐captive Asian timber elephants (Elephas maximus) and report the first evidence of age‐specific fitness declines that are driven by age‐specific associations between fitness components in a long‐lived mammal. Associations between reproduction and survival are positive in early life, but negative in later life with up to 71% of later‐life survival declines associated with investing in the production of offspring within this population of this critically endangered species.}, author = {Robinson, Matthew Richard and Mar, Khyne U and Lummaa, Virpi}, issn = {1461-023X}, journal = {Ecology Letters}, number = {3}, pages = {260--266}, publisher = {Wiley}, title = {{Senescence and age-specific trade-offs between reproduction and survival in female Asian elephants}}, doi = {10.1111/j.1461-0248.2011.01735.x}, volume = {15}, year = {2012}, } @article{7776, abstract = {We present an analysis of finite-size effects in jammed packings of N soft, frictionless spheres at zero temperature. There is a 1/N correction to the discrete jump in the contact number at the transition so that jammed packings exist only above isostaticity. As a result, the canonical power-law scalings of the contact number and elastic moduli break down at low pressure. These quantities exhibit scaling collapse with a nontrivial scaling function, demonstrating that the jamming transition can be considered a phase transition. Scaling is achieved as a function of N in both two and three dimensions, indicating an upper critical dimension of 2.}, author = {Goodrich, Carl Peter and Liu, Andrea J. and Nagel, Sidney R.}, issn = {0031-9007}, journal = {Physical Review Letters}, number = {9}, publisher = {American Physical Society}, title = {{Finite-size scaling at the jamming transition}}, doi = {10.1103/physrevlett.109.095704}, volume = {109}, year = {2012}, } @article{801, abstract = {Fungal cell walls frequently contain a polymer of mannose and galactose called galactomannan. In the pathogenic filamentous fungus Aspergillus fumigatus, this polysaccharide is made of a linear mannan backbone with side chains of galactofuran and is anchored to the plasma membrane via a glycosylphosphatidylinositol or is covalently linked to the cell wall. To date, the biosynthesis and significance of this polysaccharide are unknown. The present data demonstrate that deletion of the Golgi UDP-galactofuranose transporter GlfB or the GDP-mannose transporter GmtA leads to the absence of galactofuran or galactomannan, respectively. This indicates that the biosynthesis of galactomannan probably occurs in the lumen of the Golgi apparatus and thus contrasts with the biosynthesis of other fungal cell wall polysaccharides studied to date that takes place at the plasma membrane. Transglycosylation of galactomannan from the membrane to the cell wall is hypothesized because both the cell wall-bound and membrane-bound polysaccharide forms are affected in the generated mutants. Considering the severe growth defect of the A. fumigatus GmtA-deficient mutant, proving this paradigm might provide new targets for antifungal therapy.}, author = {Engel, Jakob and Schmalhorst, Philipp S and Routier, Françoise}, journal = {Journal of Biological Chemistry}, number = {53}, pages = {44418 -- 44424}, publisher = {American Society for Biochemistry and Molecular Biology}, title = {{Biosynthesis of the fungal cell wall polysaccharide galactomannan requires intraluminal GDP-mannose}}, doi = {10.1074/jbc.M112.398321}, volume = {287}, year = {2012}, } @article{8024, abstract = {In dynamical models of cortical networks, the recurrent connectivity can amplify the input given to the network in two distinct ways. One is induced by the presence of near-critical eigenvalues in the connectivity matrix W, producing large but slow activity fluctuations along the corresponding eigenvectors (dynamical slowing). The other relies on W not being normal, which allows the network activity to make large but fast excursions along specific directions. Here we investigate the trade-off between non-normal amplification and dynamical slowing in the spontaneous activity of large random neuronal networks composed of excitatory and inhibitory neurons. We use a Schur decomposition of W to separate the two amplification mechanisms. Assuming linear stochastic dynamics, we derive an exact expression for the expected amount of purely non-normal amplification. We find that amplification is very limited if dynamical slowing must be kept weak. We conclude that, to achieve strong transient amplification with little slowing, the connectivity must be structured. We show that unidirectional connections between neurons of the same type together with reciprocal connections between neurons of different types, allow for amplification already in the fast dynamical regime. Finally, our results also shed light on the differences between balanced networks in which inhibition exactly cancels excitation and those where inhibition dominates.}, author = {Hennequin, Guillaume and Vogels, Tim P and Gerstner, Wulfram}, issn = {1539-3755}, journal = {Physical Review E}, number = {1}, publisher = {American Physical Society}, title = {{Non-normal amplification in random balanced neuronal networks}}, doi = {10.1103/physreve.86.011909}, volume = {86}, year = {2012}, } @article{808, abstract = {Using correlated live-cell imaging and electron tomography we found that actin branch junctions in protruding and treadmilling lamellipodia are not concentrated at the front as previously supposed, but link actin filament subsets in which there is a continuum of distances from a junction to the filament plus ends, for up to at least 1 mm. When branch sites were observed closely spaced on the same filament their separation was commonly a multiple of the actin helical repeat of 36 nm. Image averaging of branch junctions in the tomograms yielded a model for the in vivo branch at 2.9 nm resolution, which was comparable with that derived for the in vitro actin- Arp2/3 complex. Lamellipodium initiation was monitored in an intracellular wound-healing model and was found to involve branching from the sides of actin filaments oriented parallel to the plasmalemma. Many filament plus ends, presumably capped, terminated behind the lamellipodium tip and localized on the dorsal and ventral surfaces of the actin network. These findings reveal how branching events initiate and maintain a network of actin filaments of variable length, and provide the first structural model of the branch junction in vivo. A possible role of filament capping in generating the lamellipodium leaflet is discussed and a mathematical model of protrusion is also presented.}, author = {Vinzenz, Marlene and Nemethova, Maria and Schur, Florian and Mueller, Jan and Narita, Akihiro and Urban, Edit and Winkler, Christoph and Schmeiser, Christian and Koestler, Stefan and Rottner, Klemens and Resch, Guenter and Maéda, Yuichiro and Small, John}, journal = {Journal of Cell Science}, number = {11}, pages = {2775 -- 2785}, publisher = {Company of Biologists}, title = {{Actin branching in the initiation and maintenance of lamellipodia}}, doi = {10.1242/jcs.107623}, volume = {125}, year = {2012}, } @article{8246, abstract = {The Staphylococcus aureus cell wall stress stimulon (CWSS) is activated by cell envelope-targeting antibiotics or depletion of essential cell wall biosynthesis enzymes. The functionally uncharacterized S. aureus LytR-CpsA-Psr (LCP) proteins, MsrR, SA0908 and SA2103, all belong to the CWSS. Although not essential, deletion of all three LCP proteins severely impairs cell division. We show here that VraSR-dependent CWSS expression was up to 250-fold higher in single, double and triple LCP mutants than in wild type S. aureus in the absence of external stress. The LCP triple mutant was virtually depleted of wall teichoic acids (WTA), which could be restored to different degrees by any of the single LCP proteins. Subinhibitory concentrations of tunicamycin, which inhibits the first WTA synthesis enzyme TarO (TagO), could partially complement the severe growth defect of the LCP triple mutant. Both of the latter findings support a role for S. aureus LCP proteins in late WTA synthesis, as in Bacillus subtilis where LCP proteins were recently proposed to transfer WTA from lipid carriers to the cell wall peptidoglycan. Intrinsic activation of the CWSS upon LCP deletion and the fact that LCP proteins were essential for WTA-loading of the cell wall, highlight their important role(s) in S. aureus cell envelope biogenesis.}, author = {Dengler, Vanina and Meier, Patricia Stutzmann and Heusser, Ronald and Kupferschmied, Peter and Fazekas, Judit and Friebe, Sarah and Staufer, Sibylle Burger and Majcherczyk, Paul A. and Moreillon, Philippe and Berger-Bächi, Brigitte and McCallum, Nadine}, issn = {0378-1097}, journal = {FEMS Microbiology Letters}, number = {2}, pages = {109--120}, publisher = {Oxford University Press}, title = {{Deletion of hypothetical wall teichoic acid ligases in Staphylococcus aureus activates the cell wall stress response}}, doi = {10.1111/j.1574-6968.2012.02603.x}, volume = {333}, year = {2012}, } @article{826, abstract = {Plants exhibit a unique developmental flexibility to ever-changing environmental conditions. To achieve their profound adaptability, plants are able to maintain permanent stem cell populations and form new organs during the entire plant life cycle. Signaling substances, called plant hormones, such as auxin, cytokinin, abscisic acid, brassinosteroid, ethylene, gibberellin, jasmonic acid, and strigolactone, govern and coordinate these developmental processes. Physiological and genetic studies have dissected the molecular components of signal perception and transduction of the individual hormonal pathways. However, over recent years it has become evident that hormones do not act only in a linear pathway. Hormonal pathways are interconnected by a complex network of interactions and feedback circuits that determines the final outcome of the individual hormone actions. This raises questions about the molecular mechanisms underlying hormonal cross talk and about how these hormonal networks are established, maintained, and modulated throughout plant development.}, author = {Vanstraelen, Marleen and Eva Benková}, journal = {Annual Review of Cell and Developmental Biology}, pages = {463 -- 487}, publisher = {Annual Reviews}, title = {{Hormonal interactions in the regulation of plant development}}, doi = {10.1146/annurev-cellbio-101011-155741}, volume = {28}, year = {2012}, } @article{829, abstract = {The architecture of a plant's root system, established postembryonically, results from both coordinated root growth and lateral root branching. The plant hormones auxin and cytokinin are central endogenous signaling molecules that regulate lateral root organogenesis positively and negatively, respectively. Tight control and mutual balance of their antagonistic activities are particularly important during the early phases of lateral root organogenesis to ensure continuous lateral root initiation (LRI) and proper development of lateral root primordia (LRP). Here, we show that the early phases of lateral root organogenesis, including priming and initiation, take place in root zones with a repressed cytokinin response. Accordingly, ectopic overproduction of cytokinin in the root basal meristem most efficiently inhibits LRI. Enhanced cytokinin responses in pericycle cells between existing LRP might restrict LRI near existing LRP and, when compromised, ectopic LRI occurs. Furthermore, our results demonstrate that young LRP are more sensitive to perturbations in the cytokinin activity than are developmentally more advanced primordia. We hypothesize that the effect of cytokinin on the development of primordia possibly depends on the robustness and stability of the auxin gradient.}, author = {Bielach, Agnieszka and Podlesakova, Katerina and Peter Marhavy and Duclercq, Jérôme and Candela Cuesta and Muller, Bruno and Grunewald, Wim and Tarkowski, Petr and Eva Benková}, journal = {The Plant Cell}, number = {10}, pages = {3967 -- 3981}, publisher = {American Society of Plant Biologists}, title = {{Spatiotemporal regulation of lateral root organogenesis in Arabidopsis by cytokinin}}, doi = {10.1105/tpc.112.103044}, volume = {24}, year = {2012}, }