On the mechanism of hydrophobic association of nanoscopic solutes

The hydration behavior of two planar nanoscopic hydrophobic solutes in liquid water at normal temperature and pressure is investigated by calculating the potential of mean force between them at constant pressure as a function of the solute-solvent interaction potential. The importance of the effect of weak attractive interactions between the solute atoms and the solvent on the hydration behavior is clearly demonstrated. We focus on the underlying mechanism behind the contrasting results obtained in various recent experimental and computational studies on water near hydrophobic solutes. The length scale where crossover from a solvent separated state to the contact pair state occurs is shown to depend on the solute sizes as well as on details of the solute-solvent interaction. We find the mechanism for attractive mean forces between the plates is very different depending on the nature of the solute-solvent interaction which has implications for the mechanism of the hydrophobic effect for biomolecules.     

Phthal­imide at 120 K: perforated molecular ribbons containing three different ring motifs

Molecules of phthal­imide [1H‐iso­indole‐1,3(2H)‐dione], C₈H₅NO₂, are linked by N—H?O hydrogen bonds [H?O 2.02 Å, N?O 2.8781 (16) Å and N—H?O 167°] and by C—H?O hydrogen bonds [H?O 2.54 and 2.56 Å, C?O 3.3874 (18) and 3.4628 (19) Å, and C—H?O 149 and 159°] into molecular ribbons, which are pierced by three different ring motifs; there are two centrosymmetric R(8) rings, each containing a single hydrogen bond, N—H?O in one case and C—H?O in the other, and R(9) rings containing all three hydrogen bonds.     

On designing MAC protocols for wireless networks using directional antennas

We investigate the possibility of using directional antennas for medium access control in wireless ad hoc networks. Previous research in ad hoc networks typically assumes the use of omnidirectional antennas at all nodes. With omnidirectional antennas, while two nodes are communicating using a given channel, MAC protocols such as IEEE 802.11 require all other nodes in the vicinity to remain silent. With directional antennas, two pairs of nodes located in each other's vicinity may potentially communicate simultaneously, increasing spatial reuse of the wireless channel. Range extension due to higher gain of directional antennas can also be useful in discovering fewer hop routes. However, new problems arise when using directional beams that simple modifications to 802.11 may not be able to mitigate. This paper identifies these problems and evaluates the tradeoffs associated with them. We also design a directional MAC protocol (MMAC) that uses multihop RTSs to establish links between distant nodes and then transmits CTS, DATA, and ACK over a single hop. While MMAC does not address all the problems identified with directional communication, it is an attempt to exploit the primary benefits of beamforming in the presence of some of these problems. Results show that MMAC can perform better than IEEE 802.11, although we find that the performance is dependent on the topology and flow patterns in the system.     

Optical Virtual Private Networks: Survivability Against Multiple Link Failures

The Optical Virtual Private Networks (OVPNs) are going to be the next step of the present Internet Protocol or Multi-Protocol Label Switching-based VPNs. Since reliability and continuity of service are the major requirements in the design of OVPN, researchers are now paying more attention to its survivability issue. In this paper, we propose a highly simple approach for spreading out the lightpaths over the core optical network using shortest pair algorithm that mitigates the impact of multiple link failures in an OVPN. The special feature of the proposed Distributed Lightpath Routing algorithm lies in its simplicity and less computation for the working path as well as for the backup path.     

Revisiting Impossible Quantum Operations Using Principles of No-Signaling and Nonincrease of Entanglement Under LOCC

In this letter, we show the impossibility of the general operation introduced by Pati (Phys. Rev. A 66:062319, 2002) using two different but consistent principles (i) no-signaling (ii) non increase of entanglement under LOCC.     

Hydro­gen bonding in C-methyl­ated nitro­anilines: a room-temperature monoclinic polymorph of 4-methyl-3-nitro­aniline with Z′ = 2

The title compound, C₇H₈N₂O₂, is monoclinic (space group P2₁/n) at 295 (2) K with Z′ = 2. The two types of mol­ecule form independent C(7) chains, and the structure is related to that of the low-temperature triclinic polymorph, where Z′ = 4 in P, by a simple displacive transformation.     

Palladium‐catalyzed phosphonation of SEBS block copolymer

Phosphonic acid‐bearing styrene–ethylene/butylene–styrene (SEBS) block copolymer was synthesized by bromination and subsequent palladium‐catalyzed phosphonation of SEBS. The phosphonated block copolymer was characterized by spectroscopic, thermal, and conductivity measurements. The new polymer shows good ion‐exchange capacity of ～0.7 meq/g and proton conductivity of around 2–4 mS/cm (at room temperature and 100% relative humidity) which is in good agreement with literature value of other phosphonated materials. This value was obtained despite a relatively low degree of phosphonation, demonstrating the ability of the phase separated nature of block copolymers to promote proton conductivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5431–5441, 2008     

Steady state analysis of an M/G/1 queue with linear retrial policy and two phase service under Bernoulli vacation schedule

We consider a single server queueing system with two phases of heterogeneous service and Bernoulli vacation schedule which operate under the so called linear retrial policy. This model extends both the classical M/G/1 retrial queue with linear retrial policy as well as the M/G/1 queue with two phases of service and Bernoulli vacation model. We carry out an extensive analysis of the model.