@inbook{2336, abstract = { Now that the low temperature properties of quantum-mechanical many-body systems (bosons) at low density, ρ, can be examined experimentally it is appropriate to revisit some of the formulas deduced by many authors 4–5 decades ago, and to explore new regimes not treated before. For systems with repulsive (i.e. positive) interaction potentials the experimental low temperature state and the ground state are effectively synonymous — and this fact is used in all modeling. In such cases, the leading term in the energy/particle is 2πħ2 aρ/m where a is the scattering length of the two-body potential. Owing to the delicate and peculiar nature of bosonic correlations (such as the strange N 7/5 law for charged bosons), four decades of research failed to establish this plausible formula rigorously. The only previous lower bound for the energy was found by Dyson in 1957, but it was 14 times too small. The correct asymptotic formula has been obtained by us and this work will be presented. The reason behind the mathematical difficulties will be emphasized. A different formula, postulated as late as 1971 by Schick, holds in two dimensions and this, too, will be shown to be correct. With the aid of the methodology developed to prove the lower bound for the homogeneous gas, several other problems have been successfully addressed. One is the proof by us that the Gross-Pitaevskii equation correctly describes the ground state in the ‘traps’ actually used in the experiments. For this system it is also possible to prove complete Bose condensation and superfluidity as we have shown. On the frontier of experimental developments is the possibility that a dilute gas in an elongated trap will behave like a one-dimensional system; we have proved this mathematically. Another topic is a proof that Foldy’s 1961 theory of a high density Bose gas of charged particles correctly describes its ground state energy; using this we can also prove the N 7/5 formula for the ground state energy of the two-component charged Bose gas proposed by Dyson in 1967. All of this is quite recent work and it is hoped that the mathematical methodology might be useful, ultimately, to solve more complex problems connected with these interesting systems.}, author = {Lieb, Élliott H and Robert Seiringer and Solovej, Jan P and Yngvason, Jakob}, booktitle = {Perspectives in Analysis}, editor = {Benedicks, Michael and Jones, Peter W and Smirnov, Stanislav and Winckler, Björn}, pages = {97 -- 183}, publisher = {Springer}, title = {{The quantum-mechanical many-body problem: The Bose gas}}, doi = {10.1007/3-540-30434-7_9}, volume = {27}, year = {2005}, } @article{2359, abstract = {The validity of substituting a c-number z for the k = 0 mode operator a0 is established rigorously in full generality, thereby verifying one aspect of Bogoliubov's 1947 theory. This substitution not only yields the correct value of thermodynamic quantities such as the pressure or ground state energy, but also the value of |z|2 that maximizes the partition function equals the true amount of condensation in the presence of a gauge-symmetry-breaking term. This point had previously been elusive.}, author = {Lieb, Élliott H and Robert Seiringer and Yngvason, Jakob}, journal = {Physical Review Letters}, number = {8}, publisher = {American Physical Society}, title = {{Justification of c-number substitutions in bosonic hamiltonians}}, doi = {10.1103/PhysRevLett.94.080401}, volume = {94}, year = {2005}, } @article{2361, abstract = {The strong subadditivity of entropy plays a key role in several areas of physics and mathematics. It states that the entropy S[±]=- Tr(ϱlnϱ) of a density matrix ϱ123 on the product of three Hilbert spaces satisfies S[ϱ123]- S[ϱ12]≤S[ϱ23]-S[ϱ2]. We strengthen this to S[ϱ123]-S[ϱ12] ≤αnα(S[ϱ23α]-S[ϱ2α]), where the nα are weights and the ϱ23α are partitions of ϱ23. Correspondingly, there is a strengthening of the theorem that the map A|Trexp[L+lnA] is concave. As applications we prove some monotonicity and convexity properties of the Wehrl coherent state entropy and entropy inequalities for quantum gases.}, author = {Lieb, Élliott H and Robert Seiringer}, journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, number = {6}, publisher = {American Physical Society}, title = {{Stronger subadditivity of entropy}}, doi = {10.1103/PhysRevA.71.062329}, volume = {71}, year = {2005}, } @article{2362, abstract = {Recent developments in the physics of low-density trapped gases make it worthwhile to verify old, well-known results that, while plausible, were based on perturbation theory and assumptions about pseudopotentials. We use and extend recently developed techniques to give a rigorous derivation of the asymptotic formula for the ground-state energy of a dilute gas of N fermions interacting with a short-range, positive potential of scattering length a. For spin-12 fermions, this is E∼E0+(22m)2πNa, where E0 is the energy of the noninteracting system and is the density. A similar formula holds in two dimensions (2D), with a replaced by ln(a2). Obviously this 2D energy is not the expectation value of a density-independent pseudopotential.}, author = {Lieb, Élliott H and Robert Seiringer and Solovej, Jan P}, journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, number = {5}, publisher = {American Physical Society}, title = {{Ground state energy of the low density Fermi gas}}, doi = {10.1103/PhysRevA.71.053605}, volume = {71}, year = {2005}, } @article{2427, abstract = {Intersection graphs of disks and of line segments, respectively, have been well studied, because of both practical applications and theoretically interesting properties of these graphs. Despite partial results, the complexity status of the Clique problem for these two graph classes is still open. Here, we consider the Clique problem for intersection graphs of ellipses, which, in a sense, interpolate between disks and line segments, and show that the problem is APX-hard in that case. Moreover, this holds even if for all ellipses, the ratio of the larger over the smaller radius is some prescribed number. Furthermore, the reduction immediately carries over to intersection graphs of triangles. To our knowledge, this is the first hardness result for the Clique problem in intersection graphs of convex objects with finite description complexity. We also describe a simple approximation algorithm for the case of ellipses for which the ratio of radii is bounded.}, author = {Ambühl, Christoph and Uli Wagner}, journal = {Theory of Computing Systems}, number = {3}, pages = {279 -- 292}, publisher = {Springer}, title = {{The Clique problem in intersection graphs of ellipses and triangles}}, doi = {10.1007/s00224-005-1141-6}, volume = {38}, year = {2005}, } @inproceedings{2428, abstract = {We consider an online version of the conflict-free coloring of a set of points on the line, where each newly inserted point must be assigned a color upon insertion, and at all times the coloring has to be conflict-free, in the sense that in every interval I there is a color that appears exactly once in I. We present several deterministic and randomized algorithms for achieving this goal, and analyze their performance, that is, the maximum number of colors that they need to use, as a function of the number n of inserted points. We first show that a natural and simple (deterministic) approach may perform rather poorly, requiring Ω(√n) colors in the worst case. We then modify this approach, to obtain an efficient deterministic algorithm that uses a maximum of Θ(log 2 n) colors. Next, we present two randomized solutions. The first algorithm requires an expected number of at most O(log 2 n) colors, and produces a coloring which is valid with high probability, and the second one, which is a variant of our efficient deterministic algorithm, requires an expected number of at most O(log n log log n) colors but always produces a valid coloring. We also analyze the performance of the simplest proposed algorithm when the points are inserted in a random order, and present an incomplete analysis that indicates that, with high probability, it uses only O(log n) colors. Finally, we show that in the extension of this problem to two dimensions, where the relevant ranges are disks, n colors may be required in the worst case. The average-case behavior for disks, and cases involving other planar ranges, are still open.}, author = {Fiat, Amos and Levy, Meital B and Matoušek, Jiří and Pach, Elchanan M and Sharir, Micha and Smorodinsky, Shakhar and Uli Wagner and Welzl, Emo}, pages = {545 -- 554}, publisher = {SIAM}, title = {{Online conflict-free coloring for intervals}}, doi = {10.1137/S0097539704446682}, year = {2005}, } @article{2455, abstract = {Local accumulation of the plant growth regulator auxin mediates pattern formation in Arabidopsis roots and influences outgrowth and development of lateral root- and shoot-derived primordia. However, it has remained unclear how auxin can simultaneously regulate patterning and organ outgrowth and how its distribution is stabilized in a primordium-specif ic manner. Here we show that five PIN genes collectively control auxin distribution to regulate cell division and cell expansion in the primary root. Furthermore, the joint action of these genes has an important role in pattern formation by focusing the auxin maximum and restricting the expression domain of PLETHORA (PLT) genes, major determinants for root stem cell specification. In turn, PLT genes are required for PIN gene transcription to stabilize the auxin maximum at the distal root tip. Our data reveal an interaction network of auxin transport facilitators and root fate determinants that control patterning and growth of the root primordium.}, author = {Billou, Ikram and Xu, Jian and Wildwater, Marjolein and Willemsen, Viola and Paponov, Ivan A and Jirí Friml and Heldstra, Renze and Aida, Mitsuhiro and Palme, Klaus J and Scheres, Ben}, journal = {Nature}, number = {7021}, pages = {39 -- 44}, publisher = {Nature Publishing Group}, title = {{The PIN auxin efflux facilitator network controls growth and patterning in Arabidopsis roots}}, doi = {10.1038/nature03184}, volume = {433}, year = {2005}, } @inbook{2463, author = {Dubová, J and Hejátko, Jan and Jirí Friml}, booktitle = {Encyclopedia of Molecular Cell Biology and Molecular Medicine}, editor = {Meyers, Robert A}, pages = {249 -- 295}, publisher = {Wiley-Blackwell}, title = {{Reproduction, plants}}, doi = {10.1002/3527600906}, volume = {12}, year = {2005}, } @inbook{2464, author = {Jirí Friml and Wiśniewska, Justyna}, booktitle = {Intercellular Communication in Plants}, editor = {Fleming, Andrew J.}, publisher = {Wiley-Blackwell}, title = {{Auxin as an intercellular signal}}, volume = {16}, year = {2005}, } @article{1740, abstract = {A systematic study of the morphology of self-organized islands in the InAs/GaAs(0 0 1) and Ge/Si(0 0 1) systems is presented, based on high-resolution scanning tunneling microscopy measurements. We demonstrate that in both cases two main island families coexist: smaller pyramids bound by one type of shallow facets and larger multifaceted domes. Their structure and facet orientation are precisely determined, thus solving a highly debated argument in the case of InAs/GaAs(0 0 1). The comparison between the two material systems reveals the existence of striking similarities that extend even to the nature of island precursors and to the islands that form when depositing InGaAs or GeSi alloys. The implications of these observations on a possible universal description of the Stranski-Krastanow growth mode are discussed with respect to recent theoretical results.}, author = {Costantini, Giovanni and Rastelli, Armando and Manzano, Carlos and Acosta-Diaz, P and Georgios Katsaros and Songmuang, Rudeeson and Schmidt, Oliver G and Von Känel, Hans and Kern, Klaus}, journal = {Journal of Crystal Growth}, number = {1-4}, pages = {38 -- 45}, publisher = {Elsevier}, title = {{Pyramids and domes in the InAs/GaAs (0 0 1) and Ge/Si (0 0 1) systems}}, doi = {10.1016/j.jcrysgro.2004.12.047}, volume = {278}, year = {2005}, } @article{1741, abstract = {SiGe islands move laterally on a Si(001) substrate during in situ postgrowth annealing. This surprising behavior is revealed by an analysis of the substrate surface morphology after island removal using wet chemical etching. We explain the island motion by asymmetric surface-mediated alloying. Material leaves one side of the island by surface diffusion, and mixes with additional Si from the surrounding surface as it redeposits on the other side. Thus the island moves laterally while becoming larger and more dilute.}, author = {Denker, Ulrich and Rastelli, Armando and Stoffel, Mathieu and Tersoff, Jerry and Georgios Katsaros and Costantini, Giovanni and Kern, Klaus and Jin-Phillipp, Neng Y and Jesson, David E and Schmidt, Oliver G}, journal = {Physical Review Letters}, number = {21}, publisher = {American Physical Society}, title = {{Lateral motion of SiGe islands driven by surface-mediated alloying}}, doi = {10.1103/PhysRevLett.94.216103}, volume = {94}, year = {2005}, } @article{1742, abstract = {The effects of substrate temperature, growth rate, and postgrowth annealing on the composition of Ge islands grown on Si(001) were investigated with a combination of selective wet chemical etching and atomic force microscopy. A simple kinetic model comprising only surface diffusion processes can explain all the experimentally observed compositional profiles for pyramid and dome islands grown in the 560-620°C range. From this model three-dimensional compositional maps were extracted. By performing annealing experiments a change in the composition of the domes was observed. This could be explained as the result of the islands' movement induced by alloying-driven energy minimization. Also in this case kinetically hindered bulk diffusion processes are not needed to explain the experimental observations.}, author = {Georgios Katsaros and Costantini, Giovanni and Stoffel, Mathieu and Esteban, Rubén and Bittner, Alexander M and Rastelli, Armando and Denker, Ulrich and Schmidt, Oliver G and Kern, Klaus}, journal = {Physical Review B - Condensed Matter and Materials Physics}, number = {19}, publisher = {American Physical Society}, title = {{Kinetic origin of island intermixing during the growth of Ge on Si (001)}}, doi = {10.1103/PhysRevB.72.195320}, volume = {72}, year = {2005}, } @article{1743, abstract = {Laterally aligned multilayer GeSiSi islands grown on a patterned Si (001) substrate are disclosed by selective etching of Si in a KOH solution. This procedure allows us to visualize the vertical alignment of the islands in a three-dimensional perspective. Our technique reveals that partly coalesced double islands in the initial layer do not merge together, but instead gradually reproduce into well-separated double islands in upper layers. We attribute this effect to very thin spacer layers, which efficiently transfer the strain modulation of each island through the spacer layer to the surface. The etching rate of Si is reduced in tensile strained regions, which helps to preserve sufficient Si between the stacked islands to form a periodic array of freestanding and vertically modulated heterostructure pillars.}, author = {Zhong, Zheyang and Georgios Katsaros and Stoffel, Mathieu and Costantini, Giovanni and Kern, Klaus and Schmidt, Oliver G and Jin-Phillipp, Neng Y and Bauer, Günther}, journal = {Applied Physics Letters}, number = {26}, pages = {1 -- 3}, publisher = {American Institute of Physics}, title = {{Periodic pillar structures by Si etching of multilayer GeSi/Si islands}}, doi = {10.1063/1.2150278}, volume = {87}, year = {2005}, } @article{1744, abstract = {This paper presents optical duobinary and dicode signalling, as alternatives to the binary format, in order to improve the transmission performance in the presense of non-linear effects in a dense wavelength division multiplex (WDM) optical system. Duobinary signalling is applied to an optical system to explore the reduction of stimulated Brillouin scattering (SBS) effects. Duobinary signalling suppresses the SBS effects, and an eye-opening improvement of 0.25 to 1.2 dB is achieved relative to binary transmission over a range of input power levels. An experimental study demonstrates that duobinary modulation suppresses the four wave mixing (FWM) products of a dense WDM system by a maximum of 3 dB. The suppression is maintained over a range of channel spacings. An investigation of the impact of fibre dispersion on FWM products under binary, duobinary and dicode modulation in a dense WDM system is then performed, with interchannel spacing and optical power variation. This leads to the development of a set of guidelines for the application areas, in which it is appropriate to use duobinary or dicode modulation in WDM systems as a means of mitigating the impact of FWM.}, author = {Georgios Katsaros and Darwazeh, Izzat Z and Lane, Phil M}, journal = {IEE Proceedings - Optoelectronics}, number = {6}, pages = {344 -- 352}, publisher = {Institute of Electrical Engineers}, title = {{Non linear transmission effects in duobinary and dicode optical systems}}, doi = {10.1049/ip-opt:20045067}, volume = {152}, year = {2005}, } @article{17715, abstract = {At redshifts beyond z>6, as the mean fraction of neutral hydrogen x_HI in the intergalactic medium (IGM) increases, the line flux of Lyman alpha (Lya) emitters can be significantly suppressed, which can result in a decrease in the observed number of emitters at a given Lya flux. However, cosmological HII regions surrounding the Lya emitting galaxies alleviate these effects. We use simple models of the Lya line suppression that incorporate the presence of HII regions to predict the overall effect of the Lya absorption on the Lya luminosity function. We find, in agreement with other recent studies, that unless ionizing sources are unusually strongly clustered, a fully neutral IGM may be inconsistent with the large abundance of confirmed z=6.5 Lya emitters. However, the presence of local HII regions prohibits placing a tight constraint on the mean neutral fraction. We find x_HI < 0.25; the presence of strong winds and/or the clustering of ionizing sources would further weaken this constraint. We conclude that the evolution of the Lya LF is consistent with reionization occurring near this redshift. Finally, we suggest that a measurement of observed Lya line width as a function of the Lya luminosity, in a future, larger sample of Lya emitters, may serve as a robust diagnostic of the neutral fraction in the IGM.}, author = {Haiman, Zoltán and Cen, Renyue}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {627--631}, publisher = {American Astronomical Society}, title = {{Constraining reionization with the evolution of the luminosity function of Lyα emitting galaxies}}, doi = {10.1086/428645}, volume = {623}, year = {2005}, } @article{17720, abstract = {We revisit the possibility of detecting an extrasolar planet around a background star as it crosses the fold caustic of a foreground binary lens. During such an event, the planet's flux can be magnified by a factor of ~100 or more. The detectability of the planet depends strongly on the orientation of its orbit relative to the caustic. If the source star is inside the intercaustic region, detecting the caustic-crossing planet is difficult against the magnified flux of its parent star. In the more favorable configuration, when the star is outside the intercaustic region when the planet crosses the caustic, a close-in Jupiter-like planet around a Sun-like star at a distance of 8 kpc is detectable in 8 minute integrations with a 10 m telescope at maximal signal-to-noise ratio (S/N) ~15 for phase angle ϕ ~ 10°. In this example, we find further that the presence of methane, at its measured abundance in Jupiter, and/or water, sodium, and potassium, at the abundances expected in theoretical atmosphere models of close-in Jupiters, could be inferred from a nondetection of the planet in strong broad absorption bands at 0.6-1.4 μm caused by these compounds, accompanied by a S/N ~ 10 detection in adjacent bands. We conclude that future generations of large telescopes might be able to probe the composition of the atmospheres of distant extrasolar planets.}, author = {Spiegel, David S. and Zamojski, Michel and Gersch, Alan and Donovan, Jennifer and Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, pages = {478--486}, publisher = {American Astronomical Society}, title = {{Can we probe the atmospheric composition of an extrasolar planet from its reflection spectrum in a high‐magnification microlensing event?}}, doi = {10.1086/430696}, volume = {628}, year = {2005}, } @article{17731, abstract = {In cosmological structure formation models, massive non-linear objects in the process of formation, such as galaxy clusters, are surrounded by large-scale shocks at or around the expected virial radius. Direct observational evidence for such virial shocks is currently lacking, but we show here that their presence can be inferred from future, high resolution, high-sensitivity observations of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters. We study the detectability of virial shocks in mock SZ maps, using simple models of cluster structure (gas density and temperature distributions) and noise (background and foreground galaxy clusters projected along the line of sight, as well as the cosmic microwave background anisotropies). We find that at an angular resolution of 2'' and sensitivity of 10 micro K, expected to be reached at ~ 100 GHz frequencies in a ~ 20 hr integration with the forthcoming ALMA instrument, virial shocks associated with massive M ~ 10^15 M_Sun clusters will stand out from the noise, and can be detected at high significance. More generally, our results imply that the projected SZ surface brightness profile in future, high-resolution experiments will provide sensitive constraints on the density profile of cluster gas.}, author = {Kocsis, Bence and Haiman, Zoltán and Frei, Zsolt}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {632--649}, publisher = {American Astronomical Society}, title = {{Can virialization shocks be detected around galaxy clusters through the Sunyaev‐Zel’dovich effect?}}, doi = {10.1086/427975}, volume = {623}, year = {2005}, } @article{17737, abstract = {Cosmological models that include suppression of the power spectrum of density fluctuations on small scales exhibit an exponential reduction of high-redshift, non-linear structures, including a reduction in the rate of gamma ray bursts (GRBs). Here we quantify the constraints that the detection of distant GRBs would place on structure formation models with reduced small-scale power. We compute the number of GRBs that could be detectable by the Swift satellite at high redshifts (z > 6), assuming that the GRBs trace the cosmic star formation history, which itself traces the formation of non-linear structures. We calibrate simple models of the intrinsic luminosity function of the bursts to the number and flux distribution of GRBs observed by the Burst And Transient Source Experiment (BATSE). We find that a discovery of high-z GRBs would imply strong constraints on models with reduced small-scale power. For example, a single GRB at z > 10, or 10 GRBs at z > 5, discovered by Swift during its scheduled two-year mission, would rule out an exponential suppression of the power spectrum on scales below R_c=0.09 Mpc (exemplified by warm dark matter models with a particle mass of m_x=2 keV). Models with a less sharp suppression of small-scale power, such as those with a red tilt or a running scalar index, n_s, are more difficult to constrain, because they are more degenerate with an increase in the power spectrum normalization, sigma_8, and with models in which star-formation is allowed in low-mass minihalos. We find that a tilt of \delta n_s ~ 0.1 is difficult to detect; however, an observed rate of 1 GRB/yr at z > 12 would yield an upper limit on the running of the spectral index, alpha = d(n_s)/d(ln k) > -0.05.}, author = {Mesinger, Andrei and Perna, Rosalba and Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, pages = {1--10}, publisher = {American Astronomical Society}, title = {{Constraints on the small‐scale power spectrum of density fluctuations from high‐redshift gamma‐ray bursts}}, doi = {10.1086/428770}, volume = {623}, year = {2005}, } @article{17761, abstract = {We explore the possibility of resolving an image of a damped Lyα (DLA) system in absorption against an extended, diffuse, background X-ray source. Typical columns of neutral hydrogen in DLA systems are high enough to block out up to ~30% of the soft X-ray flux at an observed photon energy of 0.5 keV, and we find that ~1% of the area of extended X-ray sources at z ≳ 1 have their 0.5 keV flux reduced by at least 20% because of intervening DLA systems. We discuss the observability of such absorption and find that ≳300 photons per angular resolution element are required in the 0.3-8 keV band for its detection and in order to distinguish it from intrinsic surface brightness fluctuations. For the surface brightness of the currently known high-redshift extended X-ray sources, this requires an integration time of a few megaseconds on Chandra, if the maps are smoothed spatially to ≈2'' resolution. The exact required integration time depends on the DLA system's column density, metallicity, and, most strongly, its redshift. Current X-ray telescopes are likely to detect DLA systems with N < 10^22 cm^-2 only out to z ≈ 2.3. The availability of DLA systems with a suitably high column density for a silhouette detection is currently poorly known. We suggest that at low redshifts archival data of bright X-ray point sources may be useful in constraining the high-N end of the column density distribution. We briefly discuss an alternative strategy of searching for extended X-ray sources behind known DLA systems. Although with current X-ray telescopes the detections are challenging, they will be within the reach of a routine observation with a next generation X-ray telescope, such as the X-Ray Evolving Universe Spectrometer (XEUS) or Generation-X, and will deliver novel constraints on the nature of protogalaxies.}, author = {Dijkstra, Mark and Haiman, Zoltán and Scharf, Caleb}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, pages = {85--93}, publisher = {American Astronomical Society}, title = {{On detecting the X‐ray silhouette of a damped Lyα system}}, doi = {10.1086/428766}, volume = {624}, year = {2005}, } @article{17774, abstract = {We present grism spectra taken with the Advanced Camera for Surveys (ACS) to identify 29 red sources with (i775 - z850) ≥ 0.9 in the Hubble Ultra Deep Field (HUDF). Of these, 23 are found to be galaxies at redshifts between z = 5.4 and 6.7, identified by the break at 1216 Å due to intergalactic medium (IGM) absorption; two are late-type dwarf stars with red colors; and four are galaxies with colors and spectral shapes similar to dust-reddened or old galaxies at redshifts z ≈ 1-2. This constitutes the largest uniform, flux-limited sample of spectroscopically confirmed galaxies at such faint fluxes (z850 ≤ 27.5). Many are also among the most distant spectroscopically confirmed galaxies (at redshifts up to z = 6.7). We find a significant overdensity of galaxies at redshifts z = 5.9 ± 0.2. Nearly two-thirds of the galaxies in our sample (15/23) belong to this peak. Taking into account the selection function and the redshift sensitivity of the survey, we get a conservative overdensity of at least a factor of 2 along the line of sight. The galaxies found in this redshift peak are also localized in the plane of the sky in a nonrandom manner, occupying about half of the ACS chip. Thus the volume overdensity is a factor of 4. The star formation rate derived from detected sources in this overdense region is sufficient to reionize the local IGM.}, author = {Malhotra, S. and Rhoads, J. E. and Pirzkal, N. and Haiman, Zoltán and Xu, C. and Daddi, E. and Yan, H. and Bergeron, L. E. and Wang, J. and Ferguson, H. C. and Gronwall, C. and Koekemoer, A. and Kuemmel, M. and Moustakas, L. A. and Panagia, N. and Pasquali, A. and Stiavelli, M. and Walsh, J. and Windhorst, R. A. and di Serego Alighieri, S.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {666--679}, publisher = {American Astronomical Society}, title = {{An overdensity of galaxies at z= 5.9 ± 0.2 in the Hubble Ultra Deep Field confirmed using the ACS grism}}, doi = {10.1086/430047}, volume = {626}, year = {2005}, }