Cerium(III)-Catalyzed Synthesis of Schiff Bases: A Green Approach

The reaction of primary aromatic amines with aryl aldehydes is found to be catalyzed by cerium chloride heptahydrate under solvent-free conditions to give the corresponding Schiff bases in good yields.     

Ultra‐light carbon nanotube sponge as an efficient electromagnetic shielding material in the GHz range

CVD synthesised CNT flexible sponge with density lower than 0.02 g cm^–3 has been found to serve as high performance EMI shielding material without the aid of any polymer infiltration or impregnation. Due to its extreme lightweight, the specific SE of the CNT‐sponge was found to be as high as 1100 dB cm³ g^–1, having a total SE above 20 dB in the whole 1–18 GHz range, and being able to shield by absorption. The material is the best of our knowledge this specific SE value appears to be the highest reported hitherto. Improved EM absorbers should fulfil the synergic requirements of being low reflective and highly absorptive. In our CNT‐sponges this condition is not satisfied because, although their net absorption ability is strongly remarkable, their high electrical conductivity favours the wave to be reflected at the input interface. Therefore, this sponge material would have a great potential for microwave‐frequency applications that need negligible reflection and great absorption when combined in a multilayered structure that could prevent the wave to be reflected at the input interface. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Band gap tuning in nanocomposite ZrO2–SnO2 thin film achieved through sol–gel co-deposition method

Transparent SnO₂, nanocomposite ZrO₂–SnO₂ and ZrO₂ thin films were prepared by sol–gel dip-coating technique. X-ray diffraction (XRD) spectra showed a mixture of three phases: tetragonal ZrO₂ and SnO₂ and orthorhombic ZrSnO₄. X-ray photoelectron spectroscopy (XPS) gave Zr 3d, Sn 3d and O 1s spectra of the nanocomposite ZrO₂–SnO₂ thin film which revealed the presence of oxygen vacancies in the nanocomposite ZrO₂–SnO₂ thin film. Scanning electron microscopy (SEM) observations showed that microstructure of the nanocomposite ZrO₂–SnO₂ thin film consists of uniform dispersion of isolated SnO₂ particles in ZrO₂ matrix. The band gap for the ZrO₂ was estimated to be 5.51 eV and that for the nanocomposite ZrO₂–SnO₂ film was 4.9 eV. These films demonstrated the tailoring of band gap values which can be directly employed in tuning the band gap by simply changing the relative concentration of zirconium and tin elements. Photoluminescence (PL) spectra revealed an intense emission peak at 424 nm in the nanocomposite ZrO₂–SnO₂ film which indicate the presence of oxygen vacancies in ZrSnO₄.     

NMR of heparin API: investigation of unidentified signals in the USP-specified range of 2.12–3.00 ppm

This article addresses the identification and quantification of the chemical species resulting in resonances at 2.17 and 2.25 ppm in the ¹H nuclear magnetic resonance (NMR) spectrum of pharmaceutical-grade heparin sodium. The NMR signals in question were first confirmed to arise from chemical moieties covalently attached to the heparin molecule through NMR diffusion experiments as well as chemical treatment of heparin active pharmaceutical ingredient (API) containing the resonances. The material responsible for the extra NMR signals was then demonstrated by NMR spiking studies to be something other than oversulfated chondroitin sulfate and was finally identified as an O-acetylation product of heparin through ¹³C labeling experiments with subsequent NMR analysis. The extent of O-acetylation was quantified using three orthogonal techniques: ¹H NMR, ion chromatography, and headspace gas chromatography/mass spectrometry. The results of this work showed good agreement between the three quantitative methods developed to analyze the signals in the United States Pharmacopeia-specified region of 2.12–3.00 ppm for heparin API.     

<Emphasis Type="Italic">GI</Emphasis>/<Emphasis Type="Italic">M</Emphasis>/1 type queueing-inventory systems with postponed work,reservation, cancellation and common life time

In this paper we analyze two single server queueing-inventory systems in which items in the inventory have a random common life time. On realization of common life time, all customers in the system are flushed out. Subsequently the inventory reaches its maximum level S through a (positive lead time) replenishment for the next cycle which follows an exponential distribution. Through cancellation of purchases, inventory gets added until their expiry time; where cancellation time follows exponential distribution. Customers arrive according to a Poisson process and service time is exponentially distributed. On arrival if a customer finds the server busy, then he joins a buffer of varying size. If there is no inventory, the arriving customer first try to queue up in a finite waiting room of capacity K. Finding that at full, he joins a pool of infinite capacity with probability γ (0 < γ < 1); else it is lost to the system forever. We discuss two models based on ‘transfer’ of customers from the pool to the waiting room / buffer. In Model 1 when, at a service completion epoch the waiting room size drops to preassigned number L ? 1 (1 < L < K) or below, a customer is transferred from pool to waiting room with probability p (0 < p < 1) and positioned as the last among the waiting customers. If at a departure epoch the waiting room turns out to be empty and there is at least one customer in the pool, then the one ahead of all waiting in the pool gets transferred to the waiting room with probability one. We introduce a totally different transfer mechanism in Model 2: when at a service completion epoch, the server turns idle with at least one item in the inventory, the pooled customer is immediately taken for service. At the time of a cancellation if the server is idle with none, one or more customers in the waiting room, then the head of the pooled customer go to the buffer directly for service. Also we assume that no customer joins the system when there is no item in the inventory. Several system performance measures are obtained. A cost function is discussed for each model and some numerical illustrations are presented. Finally a comparison of the two models are made.     

Controllable and Predictable Viscoelastic Behavior of 3D Boron‐Doped Multiwalled Carbon Nanotube Sponges

3D carbon nanotube (CNT)‐based macrostructures are the subject of extensive attention because the outstanding properties of 1D and 2D nanostructures have not been fully translated into key engineering applications. Generation of 3D CNT architectures with covalent junctions could endow the new materials with extraordinary mechanical properties. In this study, detailed experimental characterization and statistical comparison are carried out on 3D boron‐doped multiwalled CNT (CB_xMWNT) sponges with covalent junctions and undoped multiwalled CNT (undoped‐MWNT) sponges without junctions. By investigating the plastic, elastic, viscoelastic, and dynamic viscoelastic properties of both sponges, as well as the dependency of these mechanical properties on material morphology, the CB_xMWNT sponge is found to be a more predictable and stable material than the undoped‐MWNT sponge. Statistical comparison proves that the excellent properties of the CB_xMWNT are attributed to its “elbow‐like” junctions inside the 3D networks, which prevent permanent buckling and bundling of the CNTs under extreme loading. Thus, by optimizing the covalent junctions in 3D CNT sponges, their functional behavior can be controlled and regulated. These findings may promote applications of 3D CNT sponges in various fields, including biomedical or high‐precision devices in which lightweight, controllable, and reliable mechanical properties are always desirable.