Publications

Resonant absorbers based on plasmonic materials, metamaterials, and thin films enable spectrally selective absorption filters, where absorption is maximized at the resonance wavelength. By controlling the geometrical parameters of nano/microstructures and materials' refractive indices, resonant absorbers are designed to operate at wide range of wavelengths for applications including absorption filters, thermal emitters, thermophotovoltaic devices, and sensors. However, once resonant absorbers are fabricated, it is rather challenging to control and tune the spectral absorption response. Here, we propose and demonstrate thermally tunable infrared resonant absorbers using hybrid gold-vanadium dioxide (VO2) nanostructure arrays. Absorption intensity is tuned from 90% to 20% and 96% to 32% using hybrid gold-VO2 nanowire and nanodisc arrays, respectively, by heating up the absorbers above the phase transition temperature of VO2 (68 °C). Phase change materials such as VO2 deliver useful means of altering optical properties as a function of temperature. Absorbers with tunable spectral response can find applications in sensor and detector applications, in which external stimulus such as heat, electrical signal, or light results in a change in the absorption spectrum and intensity.

Abstract We examined puberty-specific effects on affect-related behavior and on the psychophysiology of defensive and appetitive motivation while controlling for age. Adolescents ( N = 94, ages = 12 and 13 years) viewed 75 pictures (International Affective Picture System: pleasant, neutral, and aversive) while listening to auditory probes. Startle response and postauricular (PA) reflex were collected as measures of defensive and appetitive motivation, respectively. Pubertal status and measures of anxiety/stress reaction and sensation/thrill seeking were obtained. Mid-/late pubertal adolescents showed enhanced startle amplitude across all picture valences. A Puberty × Valence interaction revealed that mid-/late pubertal adolescents showed appetitive potentiation of the PA, whereas pre-/early pubertal adolescents showed no modulation of the PA reflex. Mid-/late pubertal adolescents also scored significantly higher on measures of sensation/thrill seeking than did their pre-/early pubertal peers and puberty moderated the association between psychophysiology and behavioral measures, suggesting that it plays a role in reorganizing defensive and appetitive motivational systems.

Temperature sensitivity of thermography is boosted by over 15 times to achieve millikelvin-resolution near ambient temperature.

A new research project has been initiated in our laboratory in order to study the complex electrochemical behavior of various polyhedral boranes (polyboranes). We have studied the electrochemistry of the dodecahydrodocecaborate dianion for two different cations in anhydrous acetonitrile solutions. We have noticed interesting differences in the cyclic voltammograms for each solution. Also of interest is the effect of various concentrations of the polyboranes. For instance, a solution of triethylamine dodecahydrodocecaborate ([(CH3CH2)3NH]2B12H12) at a concentration of 1 mM exhibits an oxidation wave whose potential value is dependent on the cycle number in a cyclic voltammogram. Additionally, by varying the polyborane concentration in a solution of tetra-n- butylammonium dodecahydrododecaborate ([(CH3CH2CH2CH2)4N] 2B12H12) from 1 to 10 mM, we notice additional oxidation features occur at the higher concentrations.

We propose a practical and scalable technique for point-to-point routing in wireless sensornets. This method, called Beacon Vector Routing (BVR), assigns coordinates to nodes based on the vector of hop count distances to a small set of beacons, and then defines a distance metric on these coordinates. BVR routes packets greedily, forwarding to the next hop that is the closest (according to this beacon vector distance metric) to the destination. We evaluate this approach through a combination of high-level simulation to investigate scaling and design tradeoffs, and a prototype implementation over real testbeds as a necessary reality check.

The active sites of metalloenzymes are often deeply buried inside a hydrophobic protein sheath, which protects them from undesirable hydrolysis and polymerization reactions, allowing them to achieve their normal functions. In order to mimic the hydrophobic environment of the active sites in bacterial monooxygenases, diiron(II) compounds of the general formula [Fe2([G-3]COO)4(4-RPy)2] were prepared, where [G-3]COO- is a third-generation dendrimer-appended terphenyl carboxylate ligand and 4-RPy is a pyridine derivative. The dendrimer environment provides excellent protection for the diiron center, reducing its reactivity toward dioxygen by about 300-fold compared with analogous complexes of terphenyl carboxylate ([G-1]COO-) ligands. An FeIIFeIII intermediate was characterized by electronic, electron paramagnetic resonance, Mössbauer, and X-ray absorption spectroscopic analyses following the oxygenation of [Fe2([G-3]COO)4(4-PPy)2], where 4-PPy is 4-pyrrolidinopyridine. The results are consistent with the formation of a superoxo species. This diiron compound, in the presence of dioxygen, can oxidize external substrates.