There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti3C2Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti3C2Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti3C2Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.

Electromagnetic interference shielding with 2D transition metal carbides (MXenes)

Dilute ferromagnetic oxides having Curie temperatures far in excess of 300 K and exceptionally large ordered moments per transition-metal cation challenge our understanding of magnetism in solids. These materials are high-k dielectrics with degenerate or thermally activated n-type semiconductivity. Conventional super-exchange or double-exchange interactions cannot produce long-range magnetic order at concentrations of magnetic cations of a few percent. We propose that ferromagnetic exchange here, and in dilute ferromagnetic nitrides, is mediated by shallow donor electrons that form bound magnetic polarons, which overlap to create a spin-split impurity band. The Curie temperature in the mean-field approximation varies as (xdelta)(1/2) where x and delta are the concentrations of magnetic cations and donors, respectively. High Curie temperatures arise only when empty minority-spin or majority-spin d states lie at the Fermi level in the impurity band. The magnetic phase diagram includes regions of semiconducting and metallic ferromagnetism, cluster paramagnetism, spin glass and canted antiferromagnetism.

Donor impurity band exchange in dilute ferromagnetic oxides.

The surface and materials science of tin oxide

Synthesis of metallic nanoparticles using plant extracts.

Surface and transport studies on La0.7Ba0.3MnO3:SnO2 bilayer

Sustained release of pharmaceutical drug has been a challenge to medical practitioners for a very long time. This is a requirement of anaesthetists, endoscopic surgeons and even dentists. Though commercial bandages are already available for pain and inflammation control, their drug release mechanism is mostly unknown, and is predominantly erratic. This poses a dilemma for medical practitioners, due to which, even if it is recommended to keep patch adhered to skin for 6 hours, it is often replaced in couple of hours or many a times a good amount of undelivered drug remains in the patch and gets wasted. Combining this need for systematic release of drug through such commercial patches and the property of sustained release of drug molecules through mesoporous silica particles, led to an idea for using a coat of Silica Microparticles (SiMPs) on to these patches to achieve controlled and sustained release of drug, mainly Ketoprofen (KP) (a pain-relieving commercial drug). SiMPs were synthesised and coated with pure KP drug on one hand and on another a thin layer of SiMPs was coated on the commercial KP patch. The sustained release studies were done for duration of 6-8 hours. The structural chemistry and the interaction chemistry of the silica-trapped-KP showed that the carboxylic acidic group of hydrogen from KP makes partial bond with silica through weak van-der-Waal forces interaction and efficiency of 75 % of drug loading. The commercial KP patch showed initial burst and later erratic release. However, KP patches upon coating with SiMPs showed controlled release of drug, with the initial burst release and subsequent sustained release in the agar platform-based drug release study. Loose conjugational chemistry, with good bio-availability of SiMPs provides a fine control over the release mechanism, which probably forms a fine mesh-matrix through which the drug slowly percolates. Further, since the particles are not too small, the passage of these particles through the skin-barrier is also less-probable, thereby imparting a facilitative effect for drug passage, in a controlled fashion. Hence a simple strategy is proposed to achieve better medicinal patches for pain-control and better drug efficacy.

Studies on Control of Erratic Release of Ketoprofen from Commercial Patches for Sustained Pain-Relief Using Silica Microparticles

Nanostructured materials have generated considerable interest owing to their physical and chemical properties that differ from those of their bulk counterparts. Cadmium oxide (CdO) is an important semiconducting material with varying band gap from 2.2 to 2.9 eV used for various applications. Due to its high electrical conductivity and optical transmittance in the visible region, this material is having potential application in photovoltaic devices as well. This study focuses on the preparation and characterization of CdO (undoped and 2 % Cu-doped) produced by facile sol–gel spin coating. Effect of Cu doping on the structural, optical and morphological properties of CdO have been studied.

Effect of Copper Doping on Physical Properties of Cadmium Oxide Thin Films

We have measured the temperature (T) dependencies of the dc resistances (Rdc) and the microwave loss (Rμw) in a variety of samples of (La1−xPrx)0.7Ca0.3MnO3 while varying x from 0 to 0.4. Whereas both the sets of data exhibit maxima, the ac loss peak is much flatter and, during cooling, appears at a much lower temperature than the peak temperature in Rdc. The discrepancy, which vanishes for x=0, increases with lowering tolerance factor (t) (or increasing x). Also Rμw vs T exhibits large thermal hysteresis for x=0.4 indicating that the transition is first order. Cooling in a magnetic field of 9 kOe causes an upward shift of about 20 K in the Rμw peak, in some of the x=0.4 films, yielding a large magnetoimpedance. Further, once these films are exposed to a magnetic field at low T, they fail to recover their virginal behavior on subsequent cooling from room T. These films could be brought to their original state by annealing at high T. The discrepancy between Rdc and Rμw implies that the system is inhomogene...

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Thermal hysteresis of microwave loss in (La 1−xPrx)0.7Ca 0.3MnO3 films

The stability of a pile of steel balls formed in a thin cell is studied for different liquids and air. The dependence of the angle of repose (AOR) on the medium and the cell thickness is examined. The AOR is observed to increase considerably with a decrease in cell width. In a thin cell (width comparable to a few times the ball diameter) the AOR is seen to depend on liquid viscosity, in contrast to the case of thick cells. The viscosity dependence in thin cells is attributed to the boundary wall effects, presumably caused by the influence of viscosity on granular arching. The case of a pile formed in a thin cell in air stands out to be distinctly different as compared to the piles formed in liquids. Image analysis of sphere position distributions and intersphere cavities reveals some useful systematics. Various issues such as the surface roughness of the balls, possible air trapping in micro-cavities and related formation of liquid bridges, effects of energy of impact on pile equilibrium etc. are addressed in the analysis.

Sangeeta Kale

Papers

Surface and transport studies on La0.7Ba0.3MnO3:SnO2 bilayer

Studies on Control of Erratic Release of Ketoprofen from Commercial Patches for Sustained Pain-Relief Using Silica Microparticles

Effect of Copper Doping on Physical Properties of Cadmium Oxide Thin Films

Thermal hysteresis of microwave loss in (La 1−xPrx)0.7Ca 0.3MnO3 films

Boundary effects on the stability of thin submerged granular piles