A multi-product continuous review inventory system in stochastic environment with budget constraint

Common characteristics of inventory systems include uncertain demand and restrictions such as budgetary and storage space constraints. Several authors have examined budget constrained multi-item stochastic inventory systems controlled by continuous review policies without considering marginal review shortage costs. Existing models assume that purchasing costs are paid at the time an order is placed, which is not always the case since in some systems purchasing costs are paid when order arrive. In the latter case the maximum investment in inventory is random since the inventory level when an order arrives is a random variable. Hence payment of purchasing costs on delivery yields a stochastic budget constraint for inventory. In this paper with mixture of back orders and lost sales, we assume that mean and variance of lead time demand are known but their probability distributions are unknown. After that, we apply the minimax distribution free procedure to find the minimum expected value of the random objective function with budget constraint. The random budget constraint is transformed to crisp budget constraint by chance-constraint technique. Finally, the model is illustrated by a numerical example.     

A highly efficient bismuth salts-catalyzed route for the synthesis of α-aminophosphonates

A convenient synthesis of different types of α-amino phosphonates via one-pot solvent-free three component reactions of aldehydes, amines and phosphites catalyzed by bismuth salts has been investigated. Bismuth triflate is found to be the most effective catalyst for this reaction.     

Coupled cluster study of NMR shielding constants and spin-rotation constants in SiH4, PH3 and H2S molecules

Ab initio methods are applied to analyse the NMR shielding constants and spin-rotation constants in SiH₄, PH₃ and H₂S molecules. The electron correlation effects are studied applying the MP2 and coupled cluster perturbation approaches. The basis set convergence is examined at the same time, and the final results for the equilibrium geometries are obtained at the CCSD(T)/cc-pCVQZ level. Zero-point vibrational and temperature contributions are computed at the SCF, MP2 and CCSD level of approximation. In addition, for the shielding constants we also estimate the relativistic effects, to determine total values of the shielding of the third-row nuclei in the studied molecules. Our final results for the shielding constants at 300?K are σ (²⁹Si in SiH₄)?=?482.35?ppm, σ (³¹P in PH₃)?=?611.64?ppm and σ (³³S in H₂S)?=?736.13?ppm. These values, together with estimated corrections and error bars, can be used to determine absolute NMR shielding scales for the heavy nuclei.     

Activity-Structure Study on the Peptide Fraction of AG2: a Potent In Vitro Transfection Agent

Applied Biochemistry and Biotechnology - Gemini-based amphiphiles are candidates for biomedical applications. In fact, most of the gemini compounds described in the literature have been prepared to...     

Tailoring of horseradish peroxidase activity in cationic water-in-oil microemulsions

Horseradish peroxidase (HRP) in cationic water-in-oil (W/O) microemulsions has always been ignored in reverse micellar enzymology, mainly because cationic surfactants are inhibitors of enzyme peroxidase. In the present study, for the first time, we have successfully introduced the cationic W/O microemulsion as an attractive host for efficient HRP activity. To this notion, much improved activity of HRP was observed in the W/O microemulsion of cetyltrimethylammonium bromide (CTAB) with an increase in n-hexanol concentration and W0 ([water]/[surfactant]), presumably due to the increased interfacial area of the microemulsions. In support of our above observation, six surfactants were synthesized with an increased headgroup size where the methyl groups of CTAB were subsequently replaced by the n-propyl and 2-hydroxyethyl groups, respectively, to prepare mono-, di-, and tripropylated/hydroxyethylated n-hexadecylammonium bromide. The peroxidase activity enhanced with headgroup size and also followed an overall trend similar to that found in the case of CTAB. Possibly, the reduced positive charge density at the augmented interfacial area by means of increase, either in headgroup size, cosurfactant concentration, and/or W0, is not capable of inactivating HRP. Also, the larger space at the interface may facilitate easier solubilization of the enzyme and increase the local concentration of enzyme and substrate, leading to the higher activity of HRP. The best activity was obtained with surfactant N-hexadecyl-N,N,N-tripropylammonium bromide, the highest ever found in any cationic W/O microemulsions, being almost 3 times higher than that found in water. Strikingly, this observed highest activity is comparable with that observed in an anionic bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT)-based system, the best W/O microemulsions used for HRP.     

Water gelation of an amino acid-based amphiphile

The water immobilization by a simple amino acid-containing cationic surfactant was investigated. A variety of techniques, such as (1)H NMR spectroscopy, circular dichroism (CD), steady-state fluorescence spectroscopy, and field-emission scanning electron microscopy (FESEM) were applied to determine the formation and architecture of the hydrogel. The new gelator with a minimum gelation concentration (MGC) of 0.3 % w/v shows prolonged stability and a low melting temperature (39 degrees C). (1)H NMR experiments revealed that intermolecular hydrogen bonding between the amide groups and pi-pi stacking of the indole rings are the two regulating parameters for gelation. Furthermore, fluorescence studies with 8-anilino-1-naphthalenesulfonic acid (ANS) as the probe indicate the participation of hydrophobicity during gelation. The luminescence study using both ANS and pyrene, along with FESEM results, indicate a critical concentration, well below the MGC, at which fibres begin to form. These cross-link further to give thicker fibers, leading to the formation of a hydrogel (0.3 % w/v). This new hydrogelator expresses high supramolecular chirality, as evidenced by the CD spectra. In addition, the gelator molecule was found to be nontoxic up to a concentration of 4 mM (0.2 % w/v). The high supramolecular chirality, prolonged stability, low melting point, and biocompatibility of the molecule make it a focus of chemical and biological interest.     

Alkyl chain length dependent hydrogelation of L-tryptophan-based amphiphile

The search for low molecular weight hydrogelators (LMWHs) with varying structural motif is getting intense because of its potential application in biomedicines as well as the diversified area of nanobiotechnology. Hydrophobic interaction is one of the most crucial parameters in the design and development of such LMWHs. To this notion, a methodical investigation was carried out to find the influence of varying alkyl chain length of amphiphile on water gelation efficacy, which has been only marginally addressed in the literature to date. We have synthesized a series of low molecular weight L-tryptophan-based gelators, some of which are excellent gelator for plain water, an essential criterion for biological use. The alkyl chain induced hydrophobicity at the molecular level has remarkable influence in modulating water immobilization. Water gelation efficiency was improved more than 100 times on moving from 10 to 18 carbon atoms. The self-aggregation behavior of these thermoreversible hydrogelators investigated through different spectroscopic and microscopic techniques showed that an optimum balance between hydrophilicity and hydrophobicity is indeed essential, which can be largely regulated by varying the alkyl chain length. Thus, the study offers better understanding toward tailoring the properties of gel in plain water and thereby paving the way for potential applications.     

Aldolase Cascade Facilitated by Self-Assembled Nanotubes from Short Peptide Amphiphiles

Early evolution benefited from a complex network of reactions involving multiple C−C bond forming and breaking events that were critical for primitive metabolism. Nature gradually chose highly evolved and complex enzymes such as lyases to efficiently facilitate C−C bond formation and cleavage with remarkable substrate selectivity. Reported here is a lipidated short peptide which accesses a homogenous nanotubular morphology to efficiently catalyze C−C bond cleavage and formation. This system shows morphology-dependent catalytic rates, suggesting the formation of a binding pocket and registered enhancements in the presence of the hydrogen-bond donor tyrosine, which is exploited by extant aldolases. These assemblies showed excellent substrate selectivity and templated the formation of a specific adduct from a pool of possible adducts. The ability to catalyze metabolically relevant cascade transformations suggests the importance of such systems in early evolution.     

Corticospinal interaction during isometric compensation for modulated forces with different frequencies

Background

The zebrafish visual system is a good research model because the zebrafish retina is very similar to that of humans in terms of the morphologies and functions. Studies of the retina have been facilitated by improvements in imaging techniques. In vitro techniques such as immunohistochemistry and in vivo imaging using transgenic zebrafish have been proven useful for visualizing specific subtypes of retinal cells. In contrast, in vivo imaging using organic fluorescent molecules such as fluorescent sphingolipids allows non-invasive staining and visualization of retinal cells en masse. However, these fluorescent molecules also localize to the interstitial fluid and stain whole larvae.

Results

We screened fluorescent coumarin derivatives that might preferentially stain neuronal cells including retinal cells. We identified four coumarin derivatives that could be used for in vivo imaging of zebrafish retinal cells. The retinas of living zebrafish could be stained by simply immersing larvae in water containing 1 μg/ml of a coumarin derivative for 30 min. By using confocal laser scanning microscopy, the lamination of the zebrafish retina was clearly visualized. Using these coumarin derivatives, we were able to assess the development of the zebrafish retina and the morphological abnormalities induced by genetic or chemical interventions. The coumarin derivatives were also suitable for counter-staining of transgenic zebrafish expressing fluorescent proteins in specific subtypes of retinal cells.

Conclusions

The coumarin derivatives identified in this study can stain zebrafish retinal cells in a relatively short time and at low concentrations, making them suitable for in vivo imaging of the zebrafish retina. Therefore, they will be useful tools in genetic and chemical screenings using zebrafish to identify genes and chemicals that may have crucial functions in the retina.     

An Asymptotic Sampling Recomposition Theorem for Gaussian Signals

For any Gaussian signal and every given sampling frequency we prove an asymptotic property of type Shannon’s sampling theorem, based on normalized cardinal sines, which keeps constant the sampling frequency. We generalize the Shannon’s sampling theorem for a class of non band–limited signals which plays a central role in the signal theory, the Gaussian map is the unique function which reachs the minimum of the product of the temporal and frecuential width. This solve a conjecture stated in [1] and suggested by [3].