Loading of a krypton magneto-optical trap with two hollow laser beams in a Zeeman slower

A significant enhancement in the number of cold atoms in an atomic-beam-loaded magneto-optical trap (MOT) for metastable krypton atoms is observed when hollow laser beams are used in a Zeeman slower instead of a Gaussian laser beam. In the Zeeman slower setup, a combination of two hollow laser beams, i.e., a variable-diameter hollow beam generated using a pair of axicon lenses superimposed on a fixed-diameter hollow beam, has been used to reduce the longitudinal velocity of the atoms in the atomic beam below the capture speed of the MOT. The observed enhancement in the number of atoms in the MOT is attributed to reduced destruction of the atom cloud in the MOT and increased cooling of the off-axis atoms in the atomic beam, resulting from the use of hollow beams in the Zeeman slower.     

Access to spirocyclic oxindoles via N-heterocyclic carbene-catalyzed reactions of enals and oxindole-derived α,β-unsaturated imines

A diastereoselective access to β-lactam fused spirocyclic oxindoles and related compounds bearing all carbon spiro centers is described. This N-heterocyclic carbene-catalyzed process employed challenging β,β-disubstituted α,β-unsaturated imines to react with enals.     

Diacetoxyiodobenzene mediated one-pot synthesis of diverse carboxamides from aldehydes

A novel, one-pot, and highly facile protocol has been devised for an easy access of a series of novel glycosyl carboxamides from aldehydes using diacetoxyiodobenzene in the presence of ionic liquid at ambient temperature.     

Identification of statistical regimes and crossovers in coherent random laser emission

We measure intensity statistics and identify statistical regimes and crossovers in random lasers based on nonresonant feedback. A single parameter extracted from an α-stable Levy fit is used to characterize the intensity distributions in all regimes. Measurements made over a range of scattering strengths, excitation energies, and sample sizes enable us to demarcate three regimes of intensity statistics and the corresponding crossovers. An initial subthreshold Gaussian regime abruptly transits into a Levy regime at the random lasing threshold, which is followed by a continuous gradual crossover toward a second Gaussian regime. We find that the prominence of the Levy regime depends upon the sample size.     

Aerosol-based coherent random laser

We demonstrate coherent random lasing from an aerosol of dye-doped microdroplets in air. The aerosol is in the form of a linear array of polydisperse, arbitrarily shaped, and randomly spaced microdroplets with average dimensions of about 30 μm. Upon optical excitation, ultranarrow lasing modes were observed in the emission along the axis of the linear array, while the transverse emission exhibited intrascatterer resonance peaks. Direct spatiospectral imaging and lasing threshold studies confirmed the origin of the lasing peaks to be from spatial modes that extended over the array of the polydisperse microdroplets.     

Quantum dynamics of h(2)(+) in intense laser fields on time-dependent potential energy surfaces

We have exploited the fully time-dependent Born-Oppenheimer approximation to develop time-dependent potential energy surfaces for the lowest two states of H(2)(+) in the presence of intense, time-varying, few-cycle laser fields of 2-8 fs duration. Quantum dynamics are explored on these field-dressed, time-dependent potentials. Our results show that the potential well in the lowest-energy state of H(2)(+) (i) collapses as the laser pulse reaches its peak amplitude and (ii) regains its form on the trailing edge of the pulse, and (iii) the trapped nuclear wavepacket has a higher probability of leaking out from the well in the case of longer laser pulses. The carrier envelope phase is found to have negligible effect on the nuclear dynamics.     

Development of a tyre traction testing facility

An experimental setup comprising up of an indoor soil bin, a single wheel tester (SWT), a soil processing trolley, a drawbar pull loading device and an instrumentation unit was developed to perform traction tests in the soil bin to study the effect of soil, tyre and system parameters on the performance of tyres. The design of the single wheel tester was such that the dynamic weight reaction force is equal to that measured statically. It is a simple wheeled device, capable of testing tyres of up to 1.5 m in diameter, vertical force up to 19 kN, net pull up to 7.2 kN, torque up to 5.5 kN m, and speed up to 3.5 km/h.     

Performance prediction of animal drawn vehicle tyres in sand

Four animal drawn vehicle (ADV) tyres of 5.00–19, 6.00–19, 7.00–19 and 8.00–19 sizes were tested in sand under various but controlled conditions in an indoor soil bin. A tyre test carriage with four-bar parallel linkage was developed for accommodating a single wheel of different sizes. Performance tests were conducted at five levels of inflation pressure and load. The sand compaction level was varied in the range of 3.4–4.5 MPa/m and forward speed of the test carriage was maintained at 3.1 km/h. Performance of the tyres 7.00–19 and 8.00–19 was identical and offered less rolling resistance as compared to other tyres. However, their use in camel carts may not be recommended beyond the payload of 6 kN on single wheel with inflation pressure and sand compaction range of 172–379 kPa and 3.4 –4.5 MPa/m, respectively. Based on the experimental results, empirical models were developed to predict the performance of tyres. The accuracy of prediction of the developed empirical models was compared with that of existing semi-empirical approaches. Model with sand mobility number considered relatively simple and convenient to use in the field and yields reasonably good prediction for rolling resistance and sinkage.