A Phase-Field Model of Spiral Dendritic Growth

Domains of condensed-phase monolayers of chiral molecules exhibit a variety of interesting nonequilibrium structures when formed via pressurization. To model these domain patterns, we add a complex field describing the tilt degree of freedom to an (anisotropic) complex-phase-field solidification model. The resulting formalism allows for the inclusion of (in general, non-reflection symmetric) interactions between the tilt, the solid-liquid interface, and the bond orientation. Simulations demonstrate the ability of the model to exhibit spiral dendritic growth.Comment: text plus Four postscript figure file

Competitive metal‐coordination of hexaaminotriphenylene on Cu(111) by intrinsic copper versus extrinsic nickel adatoms

The interplay between self‐assembly and surface chemistry of 2,3,6,7,10,11‐hexaminotriphenylene (HATP) on Cu(111) was complementarily studied by high‐resolution Scanning‐Tunneling‐Microscopy (STM) and X‐ray Photoelectron Spectroscopy (XPS) under ultra‐high vacuum conditions. To shed light on competitive metal‐coordination, comparative experiments were carried out on pristine and nickel‐covered Cu(111). Directly after room temperature deposition of HATP onto pristine Cu(111) self‐assembled aggregates were observed by STM, while XPS indicated non‐deprotonated amino groups. Annealing up to 200 °C activated the progressive single deprotonation of all amino groups as indicated by chemical shifts of both N 1s and C 1s core levels in the XP spectra. This enabled the formation of topologically versatile π‐d conjugated coordination networks with intrinsic copper adatoms. The basic motif of these networks was a metal‐organic trimer, where three HATP molecules were coordinated by Cu3 clusters, as corroborated by accompanying Density Functional Theory (DFT) simulations. Additional deposition of more reactive nickel atoms resulted in both chemical and structural changes with deprotonation and formation of bis(diimino)‐Ni bonded networks already at room temperature. Even though fused hexagonal pores were observed, extended honeycomb networks remained elusive, as tentatively explained by a restricted reversibility of these metal‐organic bonds

High-power ultrafast thin disk laser oscillators and their potential for sub-100-femtosecond pulse generation

Ultrafast thin disk laser oscillators achieve the highest average output powers and pulse energies of any mode-locked laser oscillator technology. The thin disk concept avoids thermal problems occurring in conventional high-power rod or slab lasers and enables high-power TEM00 operation with broadband gain materials. Stable and self-starting passive pulse formation is achieved with semiconductor saturable absorber mirrors (SESAMs). The key components of ultrafast thin disk lasers, such as gain material, SESAM, and dispersive cavity mirrors, are all used in reflection. This is an advantage for the generation of ultrashort pulses with excellent temporal, spectral, and spatial properties because the pulses are not affected by large nonlinearities in the oscillator. Output powers close to 100W and pulse energies above 10μJ are directly obtained without any additional amplification, which makes these lasers interesting for a growing number of industrial and scientific applications such as material processing or driving experiments in high-field science. Ultrafast thin disk lasers are based on a power-scalable concept, and substantially higher power levels appear feasible. However, both the highest power levels and pulse energies are currently only achieved with Yb:YAG as the gain material, which limits the gain bandwidth and therefore the achievable pulse duration to 700 to 800fs in efficient thin disk operation. Other Yb-doped gain materials exhibit a larger gain bandwidth and support shorter pulse durations. It is important to evaluate their suitability for power scaling in the thin disk laser geometry. In this paper, we review the development of ultrafast thin disk lasers with shorter pulse durations. We discuss the requirements on the gain materials and compare different Yb-doped host materials. The recently developed sesquioxide materials are particularly promising as they enabled the highest optical-to-optical efficiency (43%) and shortest pulse duration (227fs) ever achieved with a mode-locked thin disk lase

Instabilities and disorder of the domain patterns in the systems with competing interactions

The dynamics of the domains is studied in a two-dimensional model of the microphase separation of diblock copolymers in the vicinity of the transition. A criterion for the validity of the mean field theory is derived. It is shown that at certain temperatures the ordered hexagonal pattern becomes unstable with respect to the two types of instabilities: the radially-nonsymmetric distortions of the domains and the repumping of the order parameter between the neighbors. Both these instabilities may lead to the transformation of the regular hexagonal pattern into a disordered pattern.Comment: ReVTeX, 4 pages, 3 figures (postscript); submitted to Phys. Rev. Let

Rigid Chiral Membranes

Statistical ensembles of flexible two-dimensional fluid membranes arise naturally in the description of many physical systems. Typically one encounters such systems in a regime of low tension but high stiffness against bending, which is just the opposite of the regime described by the Polyakov string. We study a class of couplings between membrane shape and in-plane order which break 3-space parity invariance. Remarkably there is only {\it one} such allowed coupling (up to boundary terms); this term will be present for any lipid bilayer composed of tilted chiral molecules. We calculate the renormalization-group behavior of this relevant coupling in a simplified model and show how thermal fluctuations effectively reduce it in the infrared.Comment: 11 pages, UPR-518T (This replaced version has fonts not used removed.

The non-coding RNA landscape of human hematopoiesis and leukemia

© The Author(s) 2017. Non-coding RNAs have emerged as crucial regulators of gene expression and cell fate decisions. However, their expression patterns and regulatory functions during normal and malignant human hematopoiesis are incompletely understood. Here we present a comprehensive resource defining the non-coding RNA landscape of the human hematopoietic system. Based on highly specific non-coding RNA expression portraits per blood cell population, we identify unique fingerprint non-coding RNAs-such as LINC00173 in granulocytes-and assign these to critical regulatory circuits involved in blood homeostasis. Following the incorporation of acute myeloid leukemia samples into the landscape, we further uncover prognostically relevant non-coding RNA stem cell signatures shared between acute myeloid leukemia blasts and healthy hematopoietic stem cells. Our findings highlight the importance of the non-coding transcriptome in the formation and maintenance of the human blood hierarchy

A state-of-the-art review of curve squeal noise: Phenomena, mechanisms, modelling and mitigation

[EN] Curve squeal is an intense tonal noise occurring when a rail vehicle negotiates a sharp curve. The phenomenon can be considered to be chaotic, with a widely differing likelihood of occurrence on different days or even times of day. The term curve squeal may include several different phenomena with a wide range of dominant frequencies and potentially different excitation mechanisms. This review addresses the different squeal phenomena and the approaches used to model squeal noise; both time-domain and frequency-domain approaches are discussed and compared. Supporting measurements using test rigs and field tests are also summarised. A particular aspect that is addressed is the excitation mechanism. Two mechanisms have mainly been considered in previous publications. In many early papers the squeal was supposed to be generated by the so-called falling friction characteristic in which the friction coefficient reduces with increasing sliding velocity. More recently the mode coupling mechanism has been raised as an alternative. These two mechanisms are explained and compared and the evidence for each is discussed. Finally, a short review is given of mitigation measures and some suggestions are offered for why these are not always successful.Squicciarini, G.; Thompson, D.; Ding, B.; Baeza González, LM. (2018). A state-of-the-art review of curve squeal noise: Phenomena, mechanisms, modelling and mitigation. Notes on Numerical Fluid Mechanics and Multidisciplinary Design. 139:3-41. https://doi.org/10.1007/978-3-319-73411-8_1S341139Anderson, D., Wheatley, N., Fogarty, B., Jiang, J., Howie, A., Potter, W.: Mitigation of curve squeal noise in Queensland, New South Wales and South Australia. In: Conference on Railway Engineering. pp. 625–636, Perth, Australia (2008)Hanson, D., Jiang, J., Dowdell, B., Dwight, R.: Curve squeal: causes, treatments and results. 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Veh. Syst. Dyn. 44(sup1), 261–271 (2006)Giménez, J.G., Alonso, A., Gómez, E.: Introduction of a friction coefficient dependent on the slip in the FastSim algorithm. Veh. Syst. Dyn. 43(4), 233–244 (2005)Chiello, O., Ayasse, J.B., Vincent, N., Koch, J.R.: Curve squeal of urban rolling stock—part 3: theoretical model. J. Sound Vib. 293(3), 710–727 (2006)Collette, C.: Importance of the wheel vertical dynamics in the squeal noise mechanism on a scaled test bench. Shock Vibr. 19(2), 145–153 (2012)Brunel, J.F., Dufrénoy, P., Naït, M., Muñoz, J.L., Demilly, F.: Transient models for curve squeal noise. J. Sound Vib. 293(3), 758–765 (2006)Glocker, C., Cataldi-Spinola, E., Leine, R.I.: Curve squealing of trains: measurement, modelling and simulation. J. Sound Vib. 324(1), 365–386 (2009)Pieringer, A.: A numerical investigation of curve squeal in the case of constant wheel/rail friction. J. Sound Vib. 333(18), 4295–4313 (2014)Pieringer, A., Kropp, W.: A time-domain model for coupled vertical and tangential wheel/rail interaction—a contribution to the modelling of curve squeal. In: Maeda, T., et al. (eds.) Noise and Vibration Mitigation for Rail Transportation Systems. NNFM, vol. 118, pp. 221–229. Springer, Heidelberg (2012)Pieringer, A., Baeza, L., Kropp. W.: Modelling of railway curve squeal including effects of wheel rotation. In: Nielsen, J.C.O., et al. (eds.) Noise and Vibration Mitigation for Rail Transportation Systems. NNFM, vol. 126, pp. 417–424. Springer, Heidelberg (2015)Zenzerovic, I., Pieringer, A., Kropp. W.: Towards an engineering model for curve squeal. In: Nielsen, J.C.O., et al. (eds.) Noise and Vibration Mitigation for Rail Transportation Systems. NNFM, vol. 126, pp. 433–440. Springer, Heidelberg (2015)Zenzerovic, I., Kropp, W., Pieringer, A.: An engineering time-domain model for curve squeal: tangential point-contact model and Green’s functions approach. J. Sound Vib. 376, 149–165 (2016)Pieringer, A., Torstensson, P.T., Giner, J., Baeza, L.: Investigation of railway curve squeal using a combination of frequency- and time-domain models. In: Anderson, D., et al. (eds.) Noise and Vibration Mitigation for Rail Transportation Systems. NNFM, vol. 139, pp 81–93. Springer, Heidelberg (2018)Chen, G.X., Xiao, J.B., Liu, Q.Y., Zhou. Z.R.: Complex eigenvalue analysis of railway curve squeal. In: Schulte-Werning, B., et al. (eds.) Noise and Vibration Mitigation for Rail Transportation Systems. NNFM, vol. 99, pp. 433–439. Springer, Heidelberg (2008)Fourie, D.J., Gräbe, P.J., Heyns, P.S., Fröhling, R.D.: Analysis of wheel squeal due to unsteady longitudinal creepage using the complex eigenvalue method. In: Anderson, D., et al. (eds.) 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Wear 265(9), 1309–1316 (2008)Fletcher, D.I., Lewis, S.: Creep curve measurement to support wear and adhesion modelling, using a continuously variable creep twin disc machine. Wear 298–299, 57–65 (2013)Fletcher, D.I.: A new two-dimensional model of rolling–sliding contact creep curves for a range of lubrication types. Proc. Inst. Mech. Eng. Part J: J. Eng. Tribol. 227(6), 529–537 (2013)Matsumoto, A., Sato, Y., Ono, H., Wang, Y., Yamamoto, M., Tanimoto, M., Oka, Y.: Creep force characteristics between rail and wheel on scaled model. Wear 253(1), 199–203 (2002)Janssens, M.H.A., van Vliet, W.J., Kooijman, P.P., De Beer, F.G.: Curve squeal of railbound vehicles (part 3): measurement method and results. In: Proceedings of Internoise, vol. 3, pp. 1568–1571, Nice, France (2000)Monk-Steel, A.D., Thompson, D.J., De Beer, F.G., Janssens, M.H.A.: An investigation into the influence of longitudinal creepage on railway squeal noise due to lateral creepage. J. 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Endogenous tumor suppressor microRNA-193b: Therapeutic and prognostic value in acute myeloid leukemia

Purpose Dysregulated microRNAs are implicated in the pathogenesis and aggressiveness of acute myeloid leukemia (AML). We describe the effect of the hematopoietic stem-cell self-renewal regulating miR-193b on progression and prognosis of AML. Methods We profiled miR-193b-5p/3p expression in cytogenetically and clinically characterized de novo pediatric AML (n = 161) via quantitative real-time polymerase chain reaction and validated our findings in an independent cohort of 187 adult patients. We investigated the tumor suppressive function of miR-193b in human AML blasts, patient-derived xenografts, and miR-193b knockout mice in vitro and in vivo. Results miR-193b exerted important, endogenous, tumor-suppressive functions on the hematopoietic system. miR-193b-3p was downregulated in several cytogenetically defined subgroups of pediatric and adult AML, and low expression served as an independent indicator for poor prognosis in pediatric AML (risk ratio 6 standard error, 20.56 6 0.23; P = .016). miR-193b-3p expression improved the prognostic value of the European LeukemiaNet risk-group stratification or a 17-gene leukemic stemness score. In knockout mice, loss of miR-193b cooperated with Hoxa9/Meis1 during leukemogenesis, whereas restoring miR-193b expression impaired leukemic engraftment. Similarly, expression of miR-193b in AML blasts from patients diminished leukemic growth in vitro and in mouse xenografts. Mechanistically, miR-193b induced apoptosis and a G1/S-phase block in various human AML subgroups by targeting multiple factors of the KIT-RAS-RAF-MEK-ERK (MAPK) signaling cascade and the downstream cell cycle regulator CCND1. Conclusion The tumor-suppressive function is independent of patient age or genetics; therefore, restoring miR-193b would assure high antileukemic efficacy by blocking the entire MAPK signaling cascade while preventing the emergence of resistance mechanisms