Making space for art: a spatial perspective of disruptive and defensive institutional work in Venezuela’s art world

The physical and material aspects of space, such as geographical distance or boundaries, have social and symbolic consequences that impact how people influence and are influenced by institutions. Social actors can however contest how space is conceived, perceived and lived, thus making space a crucial lever in the disruption and defense of institutions. However, we lack understanding of the spatial aspects of such institutional struggles. In exploring how space is leveraged in institutional work, our study foregrounds the socio-political nature of space, building on and expanding the theorization of Lefebvre. We draw on an in depth longitudinal analysis of the material, social and symbolic aspects of the spatial dimensions of disruptive and defensive institutional work over the past twenty years in Venezuela’s art world. Following the Bolivarian Revolution in the late 1990s, the incoming government transformed the organization of the national cultural landscape, resulting in a prolonged period of institutional disruption and defense. We demonstrate that actors use the material, social, and symbolic dimensions of space to challenge and maintain their key values and practices, and that those three dimensions are intertwined

Bi-stable tunneling current through a molecular quantum dot

An exact solution is presented for tunneling through a negative-U d-fold degenerate molecular quantum dot weakly coupled to electrical leads. The tunnel current exhibits hysteresis if the level degeneracy of the negative-U dot is larger than two (d>2). Switching occurs in the voltage range V1 < V < V2 as a result of attractive electron correlations in the molecule, which open up a new conducting channel when the voltage is above the threshold bias voltage V2. Once this current has been established, the extra channel remains open as the voltage is reduced down to the lower threshold voltage V1. Possible realizations of the bi-stable molecular quantum dots are fullerenes, especially C60, and mixed-valence compounds.Comment: 5 pages, 1 figure. (v2) Figure updated to compare the current hysteresis for degeneracies d=4 and d>>1 of the level in the dot, minor corrections in the text. To appear in Phys. Rev.

RELIABILITY AND INTENSITY UPGRADE FOR BROOKHAVEN 200 MeV LINAC *

Abstract Brookhaven 200 MeV H -linac has been operating for the last 44 years and providing beams to nuclear physics and isotope programs. Three linac upgrades are in progress; (a) to make machine more reliable, (b) to double the intensity by increasing the beam pulse length and, (c) to produce more uniform beam current density on the target by raster the beam on the target

Asymmetric triplex metallohelices with high and selective activity against cancer cells

Small cationic amphiphilic α-helical peptides are emerging as agents for the treatment of cancer and infection, but they are costly and display unfavourable pharmacokinetics. Helical coordination complexes may offer a three-dimensional scaffold for the synthesis of mimetic architectures. However, the high symmetry and modest functionality of current systems offer little scope to tailor the structure to interact with specific biomolecular targets, or to create libraries for phenotypic screens. Here, we report the highly stereoselective asymmetric self-assembly of very stable, functionalized metallohelices. Their anti-parallel head-to-head-to-tail ‘triplex’ strand arrangement creates an amphipathic functional topology akin to that of the active sub-units of, for example, host-defence peptides and ​p53. The metallohelices display high, structure-dependent toxicity to the human colon carcinoma cell-line HCT116 ​p53++, causing dramatic changes in the cell cycle without DNA damage. They have lower toxicity to human breast adenocarcinoma cells (MDA-MB-468) and, most remarkably, they show no significant toxicity to the bacteria methicillin-resistant Staphylococcus aureus and Escherichia coli. At a glanc

Oscillatory Shear Flow-Induced Alignment of Lamellar Melts of Hydrogen-Bonded Comb Copolymer Supramolecules

In this work we present the orientational behavior of comb copolymer-like supramolecules P4VP(PDP)1.0, obtained by hydrogen bonding between poly(4-vinylpyridine) and pentadecylphenol, during large-amplitude oscillatory shear flow experiments over a broad range of frequencies (0.001-10 Hz). The alignment diagram, presenting the macroscopic alignment in T/TODT vs ω/ωc, contains three regions of parallel alignment separated by a region of perpendicular alignment. For our material, the order-disorder temperature TODT = 67 °C and ωc, the frequency above which the distortion of the chain conformation dominates the materials’ viscoelasticity, is around 0.1 Hz at 61 °C. For the first time flipping from a pure transverse alignment via biaxial transverse/perpendicular alignment to a perpendicular alignment as a function of the strain amplitude was found.

Walking a Supramolecular Tightrope: A Self-Assembled Dodecamer from an 8-Aryl-2′-deoxyguanosine Derivative

Guanosine quadruplexes (GQs) have emerged in recent years as key players in the development of promising functional nanostruc-tures.1 GQs are formed by the self-assembly of guanosine subunits into planar tetramers (G-tetrads) that stack on each other, assisted by the complexation of a metal cation such as K+ or Na+. Alternatively, GQs can also form via the folding of G-rich oligonucleotides (e.g., DNA, RNA) leading to monomeric, dimeric, and tetrameric structures via the association of one, two, or four oligonucleotides, respectively.1d,2 In the latter, the number of G-tetrads is primarily controlled by the sequence (intrinsic param-eter) of the oligonucleotide, whereas, in the former, such control can be primarily achieved by adjusting extrinsic parameters (e.g., concentration, temperature, solvent,3 the cation template,4 and/or its counteranion5). Controlling the molecularity via intrinsic parameters (i.e., structural information in the supramolecula

Current hysteresis and memory effect in a molecular quantum dot with strong electron-vibron interaction

Theory of current hysteresis for tunneling through a molecular quantum dot (MQD) with strong electron-vibron interactions and attractive electron-electron correlations is developed. The dot is modeled as a d-fold degenerate energy level weakly coupled to the leads. The effective attractive interaction between polarons in the dot results in a "switching" phenomenon in the current-voltage characteristics when d>2, in agreement with the results for the phenomenological negative-U model. The degenerate MQD with strong electron-vibron coupling has two stable current states in certain interval of the bias voltage below some critical temperature.Comment: 8 pages, 4 figure

Post-assembly modification of kinetically metastable Fe(II)2L3 triple helicates.

We report the covalent post-assembly modification of kinetically metastable amine-bearing Fe(II)2L3 triple helicates via acylation and azidation. Covalent modification of the metastable helicates prevented their reorganization to the thermodynamically favored Fe(II)4L4 tetrahedral cages, thus trapping the system at the non-equilibrium helicate structure. This functionalization strategy also conveniently provides access to a higher-order tris(porphyrinatoruthenium)-helicate complex that would be difficult to prepare by de novo ligand synthesis.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC). D.A.R. acknowledges the Gates Cambridge Trust for Ph.D. (Gates Cambridge Scholarship) and conference funding.This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/ja5042397