2,2′-Dinitro-5,5′-dithio­dibenzoic acid

In the title compound, C14H8N2O8S2, the asymmetric unit contains two independent 2,2′-dinitro-5,5′-dithio­dibenzoic acid (Dina) mol­ecules with roughly the same conformation. In the crystal structure, strong inter­molecular O—H⋯O hydrogen bonds link the organic mol­ecules into a one-dimensional zigzag chain along the a axis. The dihedral angles between the two aromatic rings [109.3 (2) and 103.1 (3)°] are larger than that (88.95°) observed in a structure of the compound with a solvent water mol­ecule [Shefter & Kalman (1969), J. Chem. Soc. D, p. 1027]. Such a difference may be explained by the occurrence of O—H⋯O hydrogen bonds involving the water mol­ecule in the previously reported structure

Never breaking quasi-periodic solutions of weakly nonlinear gas dynamics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1997.Includes bibliographical references (p. 107-108).by Michael G. Shefter.Ph.D

A triclinic modification of 5,5′-dinitro-2,2′-dithio­dipyridine

The asymmetric unit of the title compound, C10H6N4O4S2, contains two independent but similar mol­ecules. The structure is a triclinic polymorph of the monoclinic structure reported previously [Brito, Mundaca, Cárdenas, López-Rodríguez & Vargas (2007 ▶). Acta Cryst. E63, o3351–o3352]. The most obvious difference between the two polymorphs is the C—S—S—C torsion angle [−80.13 (16), −79.8 (2) and 0° for the two mol­ecules of the triclinic polymorph and the monoclinic polymorph, respectively]. The crystal structure of the title compound has two intra­molecular C—H⋯S inter­actions with average H⋯S distances of 2.69 Å, whereas this kind of inter­action is not evident in the monoclinic polymorph

A rarefaction-tracking method for hyperbolic conservation laws

We present a numerical method for scalar conservation laws in one space dimension. The solution is approximated by local similarity solutions. While many commonly used approaches are based on shocks, the presented method uses rarefaction and compression waves. The solution is represented by particles that carry function values and move according to the method of characteristics. Between two neighboring particles, an interpolation is defined by an analytical similarity solution of the conservation law. An interaction of particles represents a collision of characteristics. The resulting shock is resolved by merging particles so that the total area under the function is conserved. The method is variation diminishing, nevertheless, it has no numerical dissipation away from shocks. Although shocks are not explicitly tracked, they can be located accurately. We present numerical examples, and outline specific applications and extensions of the approach.Comment: 21 pages, 7 figures. Similarity 2008 conference proceeding

Polymorphs and hydrates of acyclovir

Acyclovir (ACV) has been commonly used as an antiviral for decades. Although the crystal structure of the commercial form, a 3:2 ACV/water solvate, has been known since 1980s, investigation into the structure of anhydrous ACV has been limited. Here, we report the characterization of four anhydrous forms of ACV and a new hydrate in addition to the known hydrate. Two of the anhydrous forms appear as small needles and are stable to air exposure, whereas the third form is morphologically similar but quickly absorbs water from the atmosphere and converts back to the commercial form. The high-temperature modification is achieved by heating anhydrous form I above 180°C. The crystal structures of anhydrous form I and a novel hydrate are reported for the first time. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:949–963, 2011Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79417/1/22336_ftp.pd

2,4-Dithiouracil: the reproducible H-bonded structural motifs in the complexes with 18-membered crown ethers

[[abstract]]2,4-Dithiouracil (DTU) forms in the crystals the H-bonded monohydrates of a 1 : 1 : 1 ratio with 18-crown-6 (18C6) 1, cis,syn,cis-isomer of dicyclohexano-18-crown-6 (DCH6A) 2, and benzo-18-crown-6 (B18C6) 3, while the anhydrous adduct with cis,anti,cis-isomer of dicyclohexano-18-crown-6 (DCH6B) 4 is of a 2 : 1 ratio. In 1–3 the components reproducibly alternate in the chains, while in 4 the chains are built of the alternative centrosymmetric dimers of 2,4-dithiouracil and the molecules of the cis,anti,cis-isomer of dicyclohexano-18-crown-6.[[journaltype]]國外[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子版[[countrycodes]]GB

Party patronage in contemporary democracies: results from an expert survey in 22 countries from five regions

This Research Note presents a new dataset of party patronage in 22 countries from five regions. The data was collected based on the same methodology to compare patterns of patronage within countries, across countries and across world regions that are usually studied separately. The Note addresses three research questions that are at the center of debates on party patronage, which is understood as the power of political parties to make appointments to the public and semi-public sector: the scope of patronage, the underlying motivations, and the criteria on the basis of which appointees are selected. The exploration of the dataset shows that party patronage is, to a different degree, widespread across all regions. The data further shows differences between policy areas, types of institutions such as government ministries, agencies and state-owned enterprises, and higher, middle and lower ranks of the bureaucracy. It is demonstrated that the political control of policy-making and implementation is the most common motivation for making political appointments. However, in countries with a large scope of patronage, appointments serve the purpose of both political control and rewarding supporters in exchange for votes and services. Finally, the data shows that parties prefer to select appointees who are characterized by political and personal loyalty as well as professional competence