Computer-enhanced polarized video microscopy has been used to study the discrete layer-by-layer surface ordering transitions of freely suspended films 4-($n$-nonyloxy) benzylidene-4-($n$-butyl) aniline (9O.4). Stable tilted hexatic smectic-$I$ layers form on both free surfaces 2D-liquid smectic-$A$ interior in a monolayer, bilayer, trilayer,...sequence as $T\ensuremath{\rightarrow}{T}_{c}$. The appearance first ten is described very well by simple power-law form,...

Psychro-active bacteria, important constituents of polar ecosystems, have a unique ability to remain active at temperatures below 0 degrees C, yet it is not known what extent the composition their outer cell surfaces aids in low-temperature viability. In this study, aqueous suspensions five strains Arctic psychro-active marine bacteria (PAMB) (mostly sea-ice isolates), were characterized by surface-enhanced Raman spectroscopy (SERS) and compared with SERS spectra from E. coli P. aerigunosa....

X-ray diffraction has been used to study the interlayer structure of fluid freely suspended liquid-crystal films versus film thickness. The observed scattering is described extremely well by a simple density model based on predicted layer fluctuation ${\mathrm{\ensuremath{\sigma}}}_{\mathit{i}}$ and tilt angle ${\mathrm{\ensuremath{\varphi}}}_{\mathit{i}}$ profiles. data determine individual ${\mathrm{\ensuremath{\sigma}}}_{\mathit{i}}$'s about \ifmmode\pm\else\textpm\fi{}0.1 \AA{},...

We have studied the sublimation and breakup of single 100–200 μm frost particles levitated electrically at temperatures in range −2°C to −30°C. Breakup rates were largely independent temperature humidity this but strongly dependent on particle shape. Irregular high aspect ratio most likely break up. Sublimation (evaporation) was accompanied by an increasing ratio. A linearized model, presented appendix, accounts for observation that thin neck regions not subject enhanced rates. Estimates...

We have developed an instrument to study the homogeneous and heterogeneous freezing of droplets in free fall. The advantages this technique are high repetition rates, telemicroscopic imaging frozen unfrozen droplets, elimination possible contamination nucleation effects induced by substrates. Droplets ejected at a rate about 5 per s from generator top temperature controlled tube. They fall stream down center tube as their images recorded using video-telemicroscopy. fraction drops is measured...

Abstract. Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for formation in clouds (Bigg and Leck, 2001), the nucleation potential most polar marine psychrophiles viruses has not been examined under conditions more closely resembling those atmosphere. In this paper, we activity (INA) several representative Antarctic sea-ice isolates Colwellia phage virus. High-resolution spectra were obtained droplets...

Surface-enhanced Raman spectroscopy (SERS) was used to detect and characterize polyatomic cations molecules that were electrosprayed into the gas phase soft-landed in vacuum on plasma-treated silver substrates. Organic dyes such as crystal violet Rhodamine B, nucleobase cytosine, nucleosides cytidine 2'-deoxycytidine immobilized by soft landing metal surfaces at kinetic energies ranging from near thermal 200 eV. While enhancing scattering 105−106-fold, surface effectively quenches...

The combined techniques of x-ray-absorption fine structure and x-ray diffraction have been used to study the strain bond distortions in epitaxial Ge-Si on Si(001). In a 31% Ge, 340-\AA{} pseudomorphic film, Ge-Ge first-neighbor lengths found be 2.44\ifmmode\pm\else\textpm\fi{}0.02 2.38\ifmmode\pm\else\textpm\fi{}0.02 \AA{}, respectively. lattice parameter perpendicular Ge-Si/Si(001) interface has ${\mathit{a}}_{\mathrm{\ensuremath{\perp}}}$=5.552\ifmmode\pm\else\textpm\fi{}0.002 agreement...

Abstract We describe experiments to investigate the first stages in evolution of small (100–200 µm) ice crystals levitated air at temperatures and humidities characteristic fully glaciated stratiform clouds. find that these conditions particle morphology is not uniquely determined by environmental temperature humidity as has commonly been assumed; other parameters, such mode initiation, appear have important effects on shape. Crystals grown from frozen droplets vapour excesses less than...

Abstract. We investigate theoretical, laboratory, and atmospheric evidence for a recently proposed hypothesis: homogeneous ice nucleation initiates at the surface, not in volume, of supercooled water drops. Using existing thermodynamic arguments, laboratory experiments, data, we conclude that embryo formation surface cannot be confirmed or disregarded. Ice rates measured as function drop size an air ambient could help distinguish between volume rates.

We have measured the light scattering intensity and homogeneous ice nucleation temperatures from water droplets containing 0-33 wt % ammonium sulfate. In these laboratory experiments, we used a free-fall freezing tube technique to determine fraction of frozen at particular droplet temperature by measuring depolarized in free-fall. Previously reported for solution concentrations greater than 5 display larger spread can be accounted experimental errors. find good agreement with lowest results...

Synchrotron x-ray diffraction has been used to study the surface and interior hexatic-to-liquid (smectic-I smectic-C) melting transitions of freely suspended liquid-crystal films N-[4'-(n-heptyl)benzylidene]-4-(n-heptyl)aniline (7O.7) five molecular layers thick. Both hexatic monolayers melt via hysteretic first-order transitions. After two undergo a transition smectic-I phase, correlation length \ensuremath{\xi} evolves smoothly from \ensuremath{\sim}100 \ensuremath{\sim}300 A\r{} with...

Abstract We have developed a double‐ring double‐disk electrodynamic balance with humidity control provided by an internal thermal diffusion chamber to study several atmospherically important processes involving 10‐200 μm ice particles. the constants needed quantify particle size and mass were determined three‐dimensional relaxation‐method calculation of non‐axisymmetric electric fields, experimental measurement onset stability using polystyrene latex microspheres known mass. levitated frost...

The surface freezing transitions in four liquid crystals (9O.4, 4O.7, 7O.7 and $\overline{14}$S5) have been studied to determine the temperature dependence finite-size behavior of their effective interface potentials. potentials are simply related attractive pair between molecules, were used probe forces that bind these crystals. Our measurements provide strong evidence for two expected theoretically crystals, long-range van der Waals short-range exponential forces, also admit possibility...

Abstract Frozen fraction measurements made using a droplet free-fall freezing tube apparatus are presented and used, along with other recent laboratory measurements, to evaluate how well both the water activity idea translated melting-point curve of Koop et al. predict homogeneous freezing-point temperatures for aqueous ammonium sulfate sulfuric acid solution droplets. The new temperature datasets agree previous lowest-temperature results solutes. lowest measured solutions shaped like curve....

Abstract. Often overlooked in studies of ice growth is how the crystal facets increase area, that is, grow laterally. This paper reports on observations and applications such lateral facet for vapor-grown air. Using a new crystal-growth chamber, we observed air pockets forming at corners when sublimated regrown. observation indicates spreading face can, under some conditions, extend as thin overhang over adjoining region. We argue this extension driven by flux surface-mobile molecules across...

The authors have measured the differential light-scattering cross sections and phase functions of single vapor-grown hexagonal ice particles levitated in an electrodynamic balance. particles, grown at temperatures −5° > T −10°C, were typically ≈50 μm diameter tended to orient with c axis either nearly vertical (parallel scattering plane normal) or horizontal (in plane). Helium–neon laser light scattered by a crystal was collected angular ranges 20°–65° 115°–160° 1024-element linear...

Abstract. Even though studies of Arctic ice forming particles suggest that a bacterial or viral source derived from open leads could be important for cloud formation in the (Bigg and Leck, 2001), nucleation potential most polar marine psychrophiles viruses has not been examined under conditions more closely resembling those atmosphere. In this paper, we activity (INA) several representative Antarctic sea-ice isolates Colwellia phage virus. High-resolution spectra were obtained droplets...

Abstract. Often overlooked in studies of ice growth is how the crystal faces grow laterally. This paper explores implications such lateral-type and it may explain air pockets other secondary features vapor-grown air. For example, using a new crystal-growth chamber, we observed forming at corners when sublimated regrown. observations support idea that lateral spreading face, its (in some cases) extension as thin overhang over adjoining region, driven by flux surface-mobile admolecules across...

Abstract. Ice crystals come in a remarkable variety of shapes and sizes that affect cloud's radiative properties. To better understand the growth these crystals, we built an improved capillary cryostat (CC2) designed to reduce potential instrumental artifacts may have influenced earlier measurements. In CC2, crystal forms at end one, two, or three well-separated, ultrafine capillaries minimize both crystal–crystal crystal–substrate interaction effects. The can be initiated using several...