Collision-induced emission of O2(b1Σ → a1Δg) in the gas phase

In flow tube studies of the quenching of O₂(b¹Σ), broad band emission of O₂(b):M collision complexes was found to appear under the discrete rotational lines of the 0–0 band of the b¹Σ → a¹Δ_g electric quadrupole transition at higher oxygen pressures and on addition of foreign gases. Bimolecular rate constants for the collision-induced emission processes have been derived from the ratio of the intensities of the discrete lines and the continuum as well as from low-resolution measurements of the relative intensities of the b → a and b → X bands as a function of O₂ and added gas pressure. They range from ≈10^?21 cm³ s^?1 for He to ≈4 × 10^?19 cm³ s^?1 for PCl₃ vapor.     

Bioactivity and chemical composition of the leaf essential oils of Zanthoxylum rhoifolium and Zanthoxylum setulosum from Monteverde, Costa Rica

The leaf essential oils of Zanthoxylum rhoifolium and Zanthoxylum setulosum (Rutaceae) from Monteverde, Costa Rica have been obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry. The principal constituents of Z. rhoifolium leaf oil were germacrene D (14.6%), limonene (12.5%), trans-2-hexenal (11.3%), beta-elemene (9.2%), 2-undecanone (9.2%), myrcene (7.9%), bicyclogermacrene (7.5%), and germacrene A (5.2%). The leaf oil of Z. setulosum was composed largely of beta-phellandrene (37.5%), beta-caryophyllene (13.7%), alpha-pinene (11.9%), germacrene D (10.9%), myrcene (5.9%), and nerolidol (5.4%). The essential oils were screened for in-vitro cytotoxic activity against Hep G2, MCF-7, and PC-3 human tumor cell lines; antibacterial activity against Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli; and for Artemia salina (brine shrimp) lethality. Neither Z. rhoifolium nor Z. setulosum leaf oils exhibited cytotoxicity or antibacterial activity. Both oils showed activity against A. salina.     

Leaf essential oil composition of five Zanthoxylum species from Monteverde, Costa Rica

The leaf essential oils from five species of Zanthoxylum (Rutaceae) from Monteverde, Costa Rica, have been obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry. The species examined include Z. fagara, Z. acuminatum, Z. melanostictum, Z. monophyllum, and an undescribed species. The most abundant classes of compounds found in Zanthoxylum leaf oils are acyclic and menthane monoterpenoids as well as simple alcohols, aldehydes, and ketones. In terms of molecular diversity, menthane and acyclic monoterpenoids, cadinane and mesocyclic sesquiterpenoids, and simple alcohols, aldehydes, and ketones dominate the essential oils of Zanthoxylum species. Monoterpenoids make up the majority of the mass of the leaf oils of Z. monophyllum, Z. acuminatum, Z. fagara, and Zanthoxylum sp. nov. Linalool, 4-terpineol, -terpineol, and trans-2-hexenol, are found in all of the Zanthoxylum species examined in this study.     

Demonstration of the N2 carrier process for LP-MOVPE of III/V''s

The suitability of an N₂ carrier in LP-MOVPE of GaInAs/InP device structures and for the growth of (Al)GaInP is investigated for the first time. Al-free GaInAs/InP HEMTs and MSM photodetectors exhibit cutoff frequencies of f_t = 135 GHz and f_max = 200 GHz and a bandwidth of 16 GHz and responsivity of 0.27 A/W, respectively. AlGaInP and GaInP layers deposited using the optimized growth conditions showed excellent structural, optical and homogeneity properties. For example X-ray diffractograms with FWHMs as low as 15–16 arcsec for 1 μm thick layers and 300 K photoluminescence mappings over full 2 inch wafers with standard deviations of ±0.23 and ±0.26 nm were obtained for both materials.     

Using matrix approximation for high-dimensional discrete optimization problems: Server consolidation based on cyclic time-series data

We consider the assignment of enterprise applications in virtual machines to physical servers, also known as server consolidation problem. Data center operators try to minimize the number of servers, but at the same time provide sufficient computing resources at each point in time. While historical workload data would allow for accurate workload forecasting and optimal allocation of enterprise applications to servers, the volume of data and the large number of resulting capacity constraints in a mathematical problem formulation renders this task impossible for any but small instances. We use singular value decomposition (SVD) to extract significant features from a large constraint matrix and provide a new geometric interpretation of these features, which allows for allocating large sets of applications efficiently to physical servers with this new formulation. While SVD is typically applied for purposes such as time series decomposition, noise filtering, or clustering, in this paper features are used to transform the original allocation problem into a low-dimensional integer program with only the extracted features in a much smaller constraint matrix. We evaluate the approach using workload data from a large data center and show that it leads to high solution quality, but at the same time allows for solving considerably larger problem instances than what would be possible without data reduction and model transform. The overall approach could also be applied to similar packing problems in service operations management.     

An Investigation of the N-Arylsulfonylation of 2-Azetidinones

N-Arylsulfonylation of 2-azetidinones can lead to the diastereoselective formation of oligomerization products. However, a simple increase of arylsulfonyl chloride concentration minimized oligomerization and allowed preparation of 1-arylsulfonyl-2-azetidinones in good yield.