A novel route to linear polycyclic compounds. Diastereoselective aldol-type reactions of α-sulfonyl carbanions

Aromatic derivatives, bifunctionalized at vicinal benzylic positions with Br and SO₂PH groups undergo one-pot annulations with unactivated cycloalkanones. The ring closure occurs by a diastereoselective aldol-type reaction of α-sulfonyl carbanions.     

Non-special Aronszajn trees on ℵω+1

We continue our research on the relative strength ofL-like combinatorial principles for successors of singular cardinals. In [3] we have shown that the existence of a λ⁺-special Aronszajn tree does not follow from that of a λ⁺-Souslin tree. It follows from [5], [4] and [6] that under G.C.H. □_λ does imply the existence of a λ⁺-Souslin tree. In [2] we show that □_λ does not follow from the existence of a λ⁺-special Aronszajn tree. Here we show that the existence of such a tree implies that of an ‘almost Souslin’ λ⁺-tree. It follows that the statement “All λ⁺-Aronszajn trees are special” implies that there are no λ⁺-Aronszajn trees.     

Heavy Traffic Limits for Queues with Many Deterministic Servers

Queueing Systems - Consider a sequence of stationary GI/D/Nqueues indexed by N↑∞, with servers' utilization $1 - \beta /\sqrt N ,\beta &;gt;0$ . For such queues we show that...     

Unifying model for several classes of two-dimensional phase transition

A relatively simple and physically transparent model based on quantum percolation and dephasing is employed to construct a global phase diagram which encodes and unifies the critical physics of the quantum Hall, "two-dimensional metal-insulator," classical percolation and, to some extent, superconductor-insulator transitions. Using real-space renormalization group techniques, crossover functions between critical points are calculated. The critical behavior around each fixed point is analyzed and some experimentally relevant puzzles are addressed.     

A new total synthesis of (±) steganone

A new total synthesis of (±) steganone was completed by a route involving the cyclization of a 2,2′-bis(bromoacyl)biaryl derivative.     

Theory of elastic π3He scattering

The pion-three-nucleon system is investigated using coupled Schrödinger equations. The coupling between the four-body (πNNN) and three-body (NNN) systems is explicitly implemented by operators for emission and absorption of the pion by each nucleon. The only simplifying assumption is the separable form for amplitudes pertaining to pure potential scattering. A set of Amado-Lovelace type equations is derived, from which the amplitude for the reaction π + ³He→ π + ³He can be evaluated. The integral equations involve intermediate integration over single relative momenta so that subsequent numerical solution is within reach.     

Polarization observables in π-d scattering

Exact calculations of vector and tensor polarizations are presented for the reaction $\text{π +}\text{d}\text{→ π +}\text{d}$ at T_π = 142 MeV. They are aimed at meeting the apparent demand raised by upcoming pertinent experiments. The effects of (i) deuteron D state, (ii) participating π-N partial waves and (iii) coupling of different π-d orbital angular momenta are found to be very important.     

From alkyl halides to alkyltrifluoromethyls using bromine trifluoride

Under the right conditions, bromine trifluoride can be a useful tool for generating new types of reactions and compounds. Thus, tris(methylthio)alkyl derivatives, easily prepared from the corresponding alkyl bromides, were converted to the corresponding RCHBrCF2SMe or RCHBrCF3 compounds. The bromine atom, however, could be easily reduced forming eventually R'CF2SMe or R'CF3. If desired, the bromine atom can serve as an entry for constructing terminal difluoroolefins.     

A model for rational abandonments from invisible queues

We propose a model for abandonments from a queue, due to excessive wait, assuming that waiting customers act rationally but without being able to observe the queue length. Customers are allowed to be heterogeneous in their preferences and consequent behavior. Our goal is to characterize customers' patience via more basic primitives, specifically waiting costs and service benefits: these two are optimally balanced by waiting customers, based on their individual cost parameters and anticipated waiting time. The waiting time distribution and patience profile then emerge as an equilibrium point of the system. The problem formulation is motivated by teleservices, prevalently telephone- and Internet-based. In such services, customers and servers are remote and queues are typically associated with the servers, hence queues are invisible to waiting customers. Our base model is the M/M/m queue, where it is shown that a unique equilibrium exists, in which rational abandonments can occur only upon arrival (zero or infinite patience for each customer). As such a behavior fails to capture the essence of abandonments, the base model is modified to account for unusual congestion or failure conditions. This indeed facilitates abandonments in finite time, leading to a nontrivial, customer dependent patience profile. Our analysis shows, quite surprisingly, that the equilibrium is unique in this case as well, and amenable to explicit calculation. This revised version was published online in June 2006 with corrections to the Cover Date.     

An algorithm to assign pedestrian groups dispersing at public gatherings based on pedestrian-traffic modelling

The minimization of weighted pedestrian and vehicle times for pedestrians dispersing at public gatherings is considered. An algorithm to solve this problem and to assign each pedestrian group to a unique selected path is developed. This algorithm considers general network where its arc values are dependent on pedestrian/traffic modelling and its nodes (intersections) have penalties.The algorithm is followed by a case study which exhibits possible pedestrian/traffic models. These experimental models yield some deterministic functional dependency between pedestrians' speed and sidewalk concentration, pedestrians' street concentration, and sidewalk concentration, and vehicles' speed and pedestrians' street concentration. If such and realistic models serve as an input to the algorithm it might contribute to reduce pedestrian/traffic conflicts and interference and hence to increase the overall safety of these two travel modes.