Trapped surfaces and emergent curved space in the Bose-Hubbard model

A Bose-Hubbard model on a dynamical lattice was introduced in previous work as a spin system analogue of emergent geometry and gravity. Graphs with regions of high connectivity in the lattice were identified as candidate analogues of spacetime geometries that contain trapped surfaces. We carry out a detailed study of these systems and show explicitly that the highly connected subgraphs trap matter. We do this by solving the model in the limit of no back-reaction of the matter on the lattice, and for states with certain symmetries that are natural for our problem. We find that in this case the problem reduces to a one-dimensional Hubbard model on a lattice with variable vertex degree and multiple edges between the same two vertices. In addition, we obtain a (discrete) differential equation for the evolution of the probability density of particles which is closed in the classical regime. This is a wave equation in which the vertex degree is related to the local speed of propagation of probability. This allows an interpretation of the probability density of particles similar to that in analogue gravity systems: matter inside this analogue system sees a curved spacetime. We verify our analytic results by numerical simulations. Finally, we analyze the dependence of localization on a gradual, rather than abrupt, fall-off of the vertex degree on the boundary of the highly connected region and find that matter is localized in and around that region.Comment: 16 pages two columns, 12 figures; references added, typos correcte

DCMF: DC & Microformats, a good marriage

This report introduces the Dublin Core Microformats (DCMF) project, a new way to use the DC element set within X/HTML. The DC microformats encode explicit semantic expressions in an X/HTML webpage, by using a specific list of terms for values of the attributes “rev” and “rel” for and elements, and “class” and “id” of other elements. Microformats can be easily processed by user agents and software, enabling a high level of interoperability. These characteristics are crucial for the growing number of social applications allowing users to participate in the Web 2.0 environment as information creators and consumers. This report reviews the origins of microformats; illustrates the coding of DC microformats using the Dublin Core Metadata Gen tool, and a Firefox extension for extraction and visualization; and discusses the benefits of creating Web services utilizing DC microformats

Role of the electric field in surface electron dynamics above the vacuum level

Scanning tunneling spectroscopy (STS) is used to study the dynamics of hot electrons trapped on a Cu(100) surface in field emission resonances (FER) above the vacuum level. Differential conductance maps show isotropic electron interference wave patterns around defects whenever their energy lies within a surface projected band gap. Their Fourier analysis reveals a broad wave vector distribution, interpreted as due to the lateral acceleration of hot electrons in the inhomogeneous tip-induced potential. A line-shape analysis of the characteristic constant-current conductance spectra permits to establish the relation between apparent width of peaks and intrinsic line-width of FERs, as well as the identification of the different broadening mechanisms.Comment: 7 pages, 4 figures, to appear in Phys. Rev.

Acquired Cold Urticaria: Clinical Features, Particular Phenotypes, and Disease Course in a Tertiary Care Center Cohort

BACKGROUND: Data about special phenotypes, natural course, and prognostic variables of patients with acquired cold urticaria (ACU) are scarce. OBJECTIVES: We sought to describe the clinical features and disease course of patients with ACU, with special attention paid to particular phenotypes, and to examine possible parameters that could predict the evolution of the disease. METHODS: This study was a retrospective chart review of 74 patients with ACU who visited a tertiary referral center of urticaria between 2005 and 2015. RESULTS: Fourteen patients (18.9%) presented with life-threatening reactions after cold exposure, and 21 (28.4%) showed negative results after cold stimulation tests (classified as atypical ACU). Nineteen patients (25.7%) achieved complete symptoms resolution at the end of the surveillance period and had no subsequent recurrences. Higher rates of atypical ACU along with a lower likelihood of achieving complete symptom resolution was observed in patients who had an onset of symptoms during childhood (P < .05). In patients with atypical ACU, shorter disease duration and lower doses of antihistamines required for achieving disease control were detected (P < .05). Age at disease onset, symptom severity, and cold urticaria threshold values were found to be related to disease evolution (P < .05). LIMITATIONS: This study was limited by its retrospective nature. CONCLUSIONS: The knowledge of the clinical predictors of the disease evolution along with the clinical features of ACU phenotypes would allow for the establishment of an early and proper therapeutic strategy

Covalent functionalization of N-doped graphene by N-alkylation

[EN] Nitrogen doped graphene was modified by N-alkylation using a combination of phase transfer catalysis and microwave irradiation. The resulting derivatives of N-doped graphene were analysed showing that the bandgap of the material varied depending on the alkylation agent used.Financial support from MINECO (Spain) (CTQ2013-48252-P and CTQ2012-32315), Junta de Comunidades de Castilla-La Mancha (PEII-2014-014-P) and Generalidad Valenciana (Prometeo 13/19) is gratefully acknowledged. M.B. thanks the MINECO for a doctoral FPI grant.Barrejon, M.; Primo Arnau, AM.; Gomez-Escalonilla, M.; Fierro, JLG.; García Gómez, H.; Langa, F. (2015). Covalent functionalization of N-doped graphene by N-alkylation. Chemical Communications. 51(95):16916-16919. https://doi.org/10.1039/c5cc06285cS16916169195195Wang, H., Maiyalagan, T., & Wang, X. (2012). Review on Recent Progress in Nitrogen-Doped Graphene: Synthesis, Characterization, and Its Potential Applications. ACS Catalysis, 2(5), 781-794. doi:10.1021/cs200652yNavalon, S., Dhakshinamoorthy, A., Alvaro, M., & Garcia, H. (2014). Carbocatalysis by Graphene-Based Materials. Chemical Reviews, 114(12), 6179-6212. doi:10.1021/cr4007347Rodríguez-Pérez, L., Herranz, M. Á., & Martín, N. (2013). The chemistry of pristine graphene. Chemical Communications, 49(36), 3721. doi:10.1039/c3cc38950bWei, D., Liu, Y., Wang, Y., Zhang, H., Huang, L., & Yu, G. (2009). Synthesis of N-Doped Graphene by Chemical Vapor Deposition and Its Electrical Properties. Nano Letters, 9(5), 1752-1758. doi:10.1021/nl803279tLee, W. J., Maiti, U. N., Lee, J. M., Lim, J., Han, T. H., & Kim, S. O. (2014). Nitrogen-doped carbon nanotubes and graphene composite structures for energy and catalytic applications. Chemical Communications, 50(52), 6818. doi:10.1039/c4cc00146jPrimo, A., Atienzar, P., Sanchez, E., Delgado, J. M., & García, H. (2012). From biomass wastes to large-area, high-quality, N-doped graphene: catalyst-free carbonization of chitosan coatings on arbitrary substrates. Chemical Communications, 48(74), 9254. doi:10.1039/c2cc34978gPrimo, A., Sánchez, E., Delgado, J. M., & García, H. (2014). High-yield production of N-doped graphitic platelets by aqueous exfoliation of pyrolyzed chitosan. Carbon, 68, 777-783. doi:10.1016/j.carbon.2013.11.068Wang, X., Sun, G., Routh, P., Kim, D.-H., Huang, W., & Chen, P. (2014). Heteroatom-doped graphene materials: syntheses, properties and applications. Chem. Soc. Rev., 43(20), 7067-7098. doi:10.1039/c4cs00141aWu, M., Cao, C., & Jiang, J. Z. (2010). Light non-metallic atom (B, N, O and F)-doped graphene: a first-principles study. Nanotechnology, 21(50), 505202. doi:10.1088/0957-4484/21/50/505202Rani, P., & Jindal, V. K. (2013). Designing band gap of graphene by B and N dopant atoms. RSC Adv., 3(3), 802-812. doi:10.1039/c2ra22664bLatorre-Sánchez, M., Primo, A., Atienzar, P., Forneli, A., & García, H. (2014). p-n Heterojunction of Doped Graphene Films Obtained by Pyrolysis of Biomass Precursors. Small, 11(8), 970-975. doi:10.1002/smll.201402278Gupta, M., Gaur, N., Kumar, P., Singh, S., Jaiswal, N. K., & Kondekar, P. N. (2015). Tailoring the electronic properties of a Z-shaped graphene field effect transistor via B/N doping. Physics Letters A, 379(7), 710-718. doi:10.1016/j.physleta.2014.12.046Kim, H. S., Kim, H. S., Kim, S. S., & Kim, Y.-H. (2014). Atomistic mechanisms of codoping-induced p- to n-type conversion in nitrogen-doped graphene. Nanoscale, 6(24), 14911-14918. doi:10.1039/c4nr05024jShirakawa, S., & Maruoka, K. (2013). Recent Developments in Asymmetric Phase-Transfer Reactions. Angewandte Chemie International Edition, 52(16), 4312-4348. doi:10.1002/anie.201206835Langa, F., & la Cruz, P. (2007). Microwave Irradiation: An Important Tool to Functionalize Fullerenes and Carbon Nanotubes. Combinatorial Chemistry & High Throughput Screening, 10(9), 766-782. doi:10.2174/138620707783018487Langa, F., de la Cruz, P., Espı́ldora, E., Garcı́a, J. J., Pérez, M. C., & de la Hoz, A. (2000). Fullerene chemistry under microwave irradiation. Carbon, 38(11-12), 1641-1646. doi:10.1016/s0008-6223(99)00284-5Kappe, C. O. (2004). Controlled Microwave Heating in Modern Organic Synthesis. Angewandte Chemie International Edition, 43(46), 6250-6284. doi:10.1002/anie.200400655Keglevich, G., Grün, A., & Bálint, E. (2013). Microwave Irradiation and Phase Transfer Catalysis in C-, O- and N-Alkylation Reactions. Current Organic Synthesis, 10(5), 751-763. doi:10.2174/1570179411310050006Ni, Z. H., Ponomarenko, L. A., Nair, R. R., Yang, R., Anissimova, S., Grigorieva, I. V., … Geim, A. K. (2010). On Resonant Scatterers As a Factor Limiting Carrier Mobility in Graphene. Nano Letters, 10(10), 3868-3872. doi:10.1021/nl101399rChang, C.-K., Kataria, S., Kuo, C.-C., Ganguly, A., Wang, B.-Y., Hwang, J.-Y., … Chen, K.-H. (2013). Band Gap Engineering of Chemical Vapor Deposited Graphene by in Situ BN Doping. ACS Nano, 7(2), 1333-1341. doi:10.1021/nn3049158Cuong, T. V., Pham, V. H., Tran, Q. T., Hahn, S. H., Chung, J. S., Shin, E. W., & Kim, E. J. (2010). Photoluminescence and Raman studies of graphene thin films prepared by reduction of graphene oxide. Materials Letters, 64(3), 399-401. doi:10.1016/j.matlet.2009.11.029Koh, Y. K., Bae, M.-H., Cahill, D. G., & Pop, E. (2010). Reliably Counting Atomic Planes of Few-Layer Graphene (n > 4). ACS Nano, 5(1), 269-274. doi:10.1021/nn102658aReina, A., Jia, X., Ho, J., Nezich, D., Son, H., Bulovic, V., … Kong, J. (2009). Large Area, Few-Layer Graphene Films on Arbitrary Substrates by Chemical Vapor Deposition. Nano Letters, 9(1), 30-35. doi:10.1021/nl801827vPan, C.-T., Hinks, J. A., Ramasse, Q. 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Clumps into Voids

We consider a spherically symmetric distribution of dust and show that it is possible, under general physically reasonable conditions, for an overdensity to evolve to an underdensity (and vice versa). We find the conditions under which this occurs and illustrate it on a class of regular Lemaitre-Tolman-Bondi solutions. The existence of this phenomenon, if verified, would have the result that the topology of density contours, assumed fixed in standard structure formation theories, would have to change and that luminous matter would not trace the dark matter distribution so well.Comment: LaTeX, 17 pages, 4 figures. Submitted to GRG 20/4/200

Interactions of Ar(9+) and metastable Ar(8+) with a Si(100) surface at velocities near the image acceleration limit

Auger LMM spectra and preliminary model simulations of Ar(9+) and metastable Ar(8+) ions interacting with a clean monocrystalline n-doped Si(100) surface are presented. By varying the experimental parameters, several yet undiscovered spectroscopic features have been observed providing valuable hints for the development of an adequate interaction model. On our apparatus the ion beam energy can be lowered to almost mere image charge attraction. High data acquisition rates could still be maintained yielding an unprecedented statistical quality of the Auger spectra.Comment: 34 pages, 11 figures, http://pikp28.uni-muenster.de/~ducree

Generating G2G_2--cosmologies with perfect fluid in dilaton gravity

We present a method for generating exact diagonal $G_2$-cosmological solutions in dilaton gravity coupled to a radiation perfect fluid and with a cosmological potential of a special type. The method is based on the symmetry group of the system of $G_2$-field equations. Several new classes of explicit exact inhomogeneous perfect fluid scalar-tensor cosmologies are presented.Comment: 10 pages, LaTe