Shielding TCP from last hop wireless losses

The pervasiveness of the transport control protocol (TCP) and the proliferation of wireless local area networks (WLAN) of the 802.11 type make the topic of TCP performance over last hop wireless networks very relevant. The Snoop protocol, a link layer solution introduced several years ago to improve the performance of TCP in this scenario, has been shown to neglect its benefits to the most widely used TCP version, TCP SACK. In this paper, we introduce the TCP SACK‐Aware Snoop protocol to address this problem. Our results indicate that the TCP SACK‐Aware Snoop protocol improves the performance of TCP SACK by around 30% compared with the original Snoop protocol and by about 8% in an environment where no TCP enhancing mechanism is in place. In addition, we introduce further modifications to the proposed protocol to make its advantages available to any TCP sender. We also show that the mechanism does not introduce unfairness among TCP sources and somewhat protects TCP against UDP traffic. Our results show important throughput improvements to all TCP versions and demonstrate that the TCP SACK‐Aware Snoop protocol shields TCP from last hop wireless losses providing throughtput values very close to the maximum possible. Copyright © 2006 John Wiley & Sons, Ltd.     

Sensitive carbohydrate detection using surface enhanced Raman tagging

Glycomic analysis is an increasingly important field in biological and biomedical research as glycosylation is one of the most important protein post-translational modifications. We have developed a new technique to detect carbohydrates using surface enhanced Raman spectroscopy (SERS) by designing and applying a Rhodamine B derivative as the SERS tag. Using a reductive amination reaction, the Rhodamine-based tag (RT) was successfully conjugated to three model carbohydrates (glucose, lactose, and glucuronic acid). SERS detection limits obtained with a 633 nm HeNe laser were ～1 nM in concentration for all the RT-carbohydrate conjugates and ～10 fmol in total sample consumption. The dynamic range of the SERS method is about 4 orders of magnitude, spanning from 1 nM to 5 μM. Ratiometric SERS quantification using isotope-substituted SERS internal references allows comparative quantifications of carbohydrates labeled with RT and deuterium/hydrogen substituted RT tags, respectively. In addition to enhancing the SERS detection of the tagged carbohydrates, the Rhodamine tagging facilitates fluorescence and mass spectrometric detection of carbohydrates. Current fluorescence sensitivity of RT-carbohydrates is ～3 nM in concentration while the mass spectrometry (MS) sensitivity is about 1 fmol, achieved with a linear ion trap electrospray ionization (ESI)-MS instrument. Potential applications that take advantage of the high SERS, fluorescence, and MS sensitivity of this SERS tagging strategy are discussed for practical glycomic analysis where carbohydrates may be quantified with a fluorescence and SERS technique and then identified with ESI-MS techniques.     

Vergleich verschiedener Methoden zur Bestimmung von Tryptophan in Proteinen

Zusammenfassung Untersuchungen überFreisetzung und Abbauvon Tryptophan bei der alkalischen Hydrolyse, sowie über die Anwendbarkeit verschiedener Bestimmungsmethoden, führten zu folgender Schlußfolgerung: Die Art der zur alkalischen Hydrolyse benutzten Alkalien ist von sekundärer Bedeutung im Vergleich zur Hydrolysedauer. Der Freisetzung des Tryptophans folgt schon bald ein Abbau, der die Tryptophan-Bestimmung in verschiedenen Proteinen in unterschiedlichem Maße beeinflußt. Für jede Hydrolyse von Proteinen zur Tryptophanbestimmung sollte daher zunächst die richtige Hydrolysezeit ermittelt Werden.Als Methoden zur Tryptophanbestimmung in alkalischen Hydrolysaten sind die Glyoxylsäure-Methode und PDAB-Methode geeignet. In bestimmten Fällen ist die Vorschaltung einer Papain-Hydrolyse angebracht, insbesondere bei Leguminosen, da hier die alkalische Hydrolyse zur Bildung gefärbter Nebenprodukte führen kann. Für die Bestimmung von freiem Tryptophan in biologischen Flüssigkeiten und allgemein dann, wenn sehr geringe Konzentrationen zu erwarten sind, ist die fluorimetrische Messung der Norharman-Bildung bei Kondensation mit Formaldehyd zu empfehlen.

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Comparison of different methods for determination of tryptophan in proteins

Summary Attempts have been made to establish suitable conditions for the liberation of trytophan from proteins, particularly legumeproteins. The hydrolyses were carried out With 3.5% HClO₄, 4N-Ba(OH)₂, 4N-KOH and papain. Photometric methods With glyoxylic acid or p-dimethylaminobenzaldehyde and one fluorometric method have been used in determining the tryptophan in hydrolysates as Well as in biological fluids.It Was found that the type of alkali used in hydrolysing proteins is of secondary importance to the duration of hydrolysis. Partial decomposition of tryptophan follows soon after its liberation, which may influence the amount of tryptophan found in different proteins to a different extent. Therefore, the proper time for alkaline hydrolysis of proteins for the determination of tryptophan should be evaluated individually and cannot be given as a general rule, Which is valid for all proteins.The glyoxylic acid and p-dimethylaminobenzaldehyde methods Were both found to be suitable for the estimation of tryptophan in alkaline hydrolysates. In some cases, especially With legumes, hydrolysis With papain lead to better results, because during alkaline hydrolysis coloured by products Were formed, which interfered With the photometric measurements. The fluorometric method of measuring the fluorescenz of norharman, Which is formed by the condensation of tryptophan with formaldehyde, followed by oxidation and decarboxylation, has been found to be applicable for the measurement of free tryptophan in biological fluids as Well as in hydrolysates, if very low concentrations of tryptophan have to be determined.

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Diese Arbeit Wurde unterstützt aus Mitteln des Forschungskreises der Ernährungsindustrie im Rahmen des Forschungsvorhabens 1049.

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Auszug aus der Dissertation vonR. R. Vangala: Die Eignung verschiedener Hydrolyseverfahren zur Ermittlung der Aminosäurezusammensetzung und der verfügbaren Aminosäuren in Nahrungsproteinen. Gießen 1968.     

Synthesis and Biological Evaluation of Imidazopyridine–Oxindole Conjugates as Microtubule‐Targeting Agents

A library of imidazopyridine–oxindole conjugates was synthesised and investigated for anticancer activity against various human cancer cell lines. Some of the tested compounds, such as 10 a , 10 e , 10 f , and 10 k , exhibited promising antiproliferative activity with GI₅₀ values ranging from 0.17 to 9.31 μM . Flow cytometric analysis showed that MCF‐7 cells treated by these compounds arrested in the G₂/M phase of the cell cycle in a concentration‐dependent manner. More particularly, compound 10 f displayed a remarkable inhibitory effect on tubulin polymerisation. All the compounds depolarised mitochondrial membrane potential and caused apoptosis. These results are further supported by the decreased phosphorylation of Akt at Ser473. Studies on embryonic development revealed that the lead compounds 10 f and 10 k caused delay in the development of zebra fish embryos. Docking of compound 10 f with tubulin protein suggested that the imidazo[1,2‐a]pyridine moiety occupies the colchicine binding site of tubulin.     

An improved high-performance liquid chromatography assay for spironolactone analysis

This study prepared an extemporaneously formulated liquid suspension dosage form (5 mg/ml) from commercially available 25 mg tablets. Stability-indicating HPLC assay procedures were established and utilized to analyze the concentration of the drug. The method proved to be a simple model since it does not contain a buffer system. The mobile phase used was the same as that suggested by the manufacturer for the storage of the column. Therefore, the solvent system saves analytical processing time, since it does not require a change in the mobile phase before or after the analysis. The analytical method has been shown to be stability-indicating. The results have shown that there is no interference from any of the degradation products obtained from stressing spironolactone by heat and extremes in pH or with the internal standard, hydrocortisone 21-acetate.     

Neurobehavioral effects of solvents and circadian rhythms

Two studies on the combined neurobehavioral effects of shiftwork and solvent exposure were performed: two-shift work/mixed solvent exposure and three-shift work/single solvent exposure (acetone). Repeated measurements of exposure, body temperature, well-being, complaints, and performance were taken during each shift and during several shift cycles. The air concentrations of the solvent mixture were clearly below and of acetone were near the occupational exposure limit values. Both the exposure quality and the circadian factor contributed to the stronger adverse effects under the three-shift condition. The results support the view that exposure effects should be studied and evaluated in relation to shift and time.     

Novel Peak‐to‐Average Power Ratio Reduction Methods for OFDM/OQAM Systems

The tone reservation method is one of the most effective pre‐distortion methods for peak‐to‐average power ratio reduction in orthogonal frequency division multiplexing (OFDM) systems. Its direct application to OFDM systems with offset quadrature amplitude modulation (OQAM) is, however, not effective. In this paper, two novel TR‐based methods are proposed, specifically designed for OFDM/OQAM systems by taking into consideration the overlapping nature of OQAM signals. These two methods have different approaches to the generation of the peak‐cancelling signal. The first one (overlapped scaling tone reservation) generates the peak‐cancelling signal using a least squares approximation algorithm with possible adjacent symbol overlap; the second one (multi‐kernel tone reservation) generates the peak‐cancelling signal by using multiple impulse‐like time domain kernels. It is shown by simulation that, when used in OFDM/OQAM systems, the proposed methods can provide better performance than the direct application of the existing controlled clipping tone reservation method, and even outperform the multi‐block tone reservation method.     

Production of orientation-patterned GaP templates using wafer fusion techniques

Nonlinear optical frequency conversion is an effective technique for generating infrared (IR) and terahertz (THz) wavelengths not readily available from existing laser sources. Birefringent materials such as LiNbO₃ are often used to generate wavelengths where gaps exist, but are unsuitable in the mid-IR, far-IR, and THz regions as these materials are often opaque in these regions. As an alternative, GaAs has been employed for frequency conversion in these regions using quasi-phase-matching (QPM) to overcome the material’s lack of birefringence. QPM has been successfully demonstrated in GaAs using fused stacks of thin alternately oriented layers or inverted orientation patterned (OP) grating templates overgrown with thick columnar GaAs layers. Although GaAs has a high nonlinear coefficient d₁₄ = 170 pm/V at 1.064 μm and good thermal conductivity (52 W/m K), it suffers from strong two-photon absorption below 1.7 μm making it inefficient when pumped with a source less than or equal to this wavelength. GaP also has a high nonlinear coefficient d₁₄ = 71 pm/V at 1.064 μm, better thermal conductivity (110 W/m K) and much lower two-photon absorption in the 1 μm region. Therefore, OPGaP is desirable for NLO applications in the mid-IR and THz that use commercially available pump lasers in the 1.06-1.55 μm wavelength range. In this work the fabrication of OPGaP templates suitable for thick columnar hydride vapor phase epitaxial growth of GaP is reported using a commercially viable wafer fusion technique.