Forced Evaporation Research Articles

Efficient production of an 87Rb F = 2, mF = 2 Bose-Einstein condensate in a hybrid trap

We have realized Bose-Einstein condensation (BEC) of 87Rb in the F=2, m_F=2 hyperfine substate in a hybrid trap, consisting of a quadrupole magnetic field and a single optical dipole beam. The symmetry axis of the quadrupole magnetic trap coincides with the optical beam axis, which gives stronger axial confinement than previous hybrid traps. After loading 2x10^6 atoms at 14 muK from a quadrupole magnetic trap into the hybrid trap, we perform efficient forced evaporation and reach the onset of BEC at a temperature of 0.5 muK and with 4x10^5 atoms. We also obtain thermal clouds of 1x10^6 atoms below 1 muK in a pure single beam optical dipole trap, by ramping down the magnetic field gradient after evaporative cooling in the hybrid trap.

Evaluación al sistema alternativo de evaporación forzada para lixiviados provenientes del botadero a cielo abierto de la ciudad de Estelí.

La realización de ésta investigación, permitió evaluar un sistema alternativo de tratamiento de los lixiviados generados en el botadero a cielo abierto de la ciudad de Estelí a partir de la evaporación forzada a través de un invernadero piloto tipo domo, en donde se demostró la viabilidad del sistema por la facilidad de las condiciones meteorológicas, permitiendo así una evaporación promedio de 0.78 cm/día y posteriormente la identificación de los gases y olores ofensivos emitidos por los lixiviados que estaban concentrados en el domo que luego de la estabilización estos olores son casi inapreciables, este monitoreo se realizó por veinte y dos días consecutivos. Del monitoreo de se logró determinar que el la temperatura para este lixiviado se encuentra en un rango de 26 º a 34 ºC con un valor promedio de 31º, siendo este rango de temperatura propio de un proceso anaerobio denominado Mesófilico. Se determinó la tendencia de los datos de evaporación de tipo exponencial. Es decir que a mayor altura de la lámina, menor es la evaporación esto se deduce debido a que se trabajó con dos láminas de lixiviados en el interior del domo, siendo la óptima de 20cm y la que se analiza en esta investigación. La implementación de éste proyecto, Evaluación al sistema alternativo de evaporación forzada para lixiviados provenientes del botadero a cielo abierto de la ciudad de Estelí; es un campo poco estudiado a nivel nacional, siendo ésta una oportunidad y técnica de investigación que puede llegar a permitir el uso de tecnologías económicas y amigables con el ambiente.

Numerical simulation of forced convective evaporation in thermal desalination units with vertical tubes

The subject of present study is a numerical simulation of transient solution of evaporation on upward flow in a two-dimensional vertical tubes by using the water as the working fluid. The heat transfer mechanisms are energy and mass transfer during the phase change based on volume of fluid model in commercial CFD software, with a user defined function. Operating conditions are specified in saturation temperature of water flow boiling. The physical properties of water are determined using inlet temperature and pressure system in saturation conditions. The characteristic of water flow boiling such as void fraction, heat transfer coefficient, and wall temperature distribution are investigated in the range of various heat fluxes. Due to agitation of vapor bubbles, the flow is turbulent which is simulated based on SST K–ω model and also the pressure implicit with splitting of operators pressure–velocity coupling scheme is used to improve the efficiency of calculation.

Photocrosslinking-induced phase separation in evaporative solvents: formation of skin layers and microspheres

We report the structure formation of films obtained via photocrosslinking of precursors during the evaporation of solvents. Although most precursor/solvent systems result in uniform dense films after the process, reaction-induced phase separation can occur in solvents with a unique combination of solubility, evaporation rate and ratio of latent heat to heat capacity. Most significantly, for such solvents, the forced convective evaporation under controlled N2 flow results in a highly hierarchical film morphology, featuring a skin layer on top of a layer of microspheres formed via a nucleation and growth mechanism. For the first time, the skin layer formed during the evaporation was directly observed after the complete evaporation of the solvent. The thickness of the skin layer is dependent on the processing parameters including the N2 flow rate, UV intensity and precursor concentrations. The skin layer formation could be suppressed by addition of non-solvent, in which case the characteristic morphology resulted from dominant spinodal decomposition. A model is presented that can qualitatively describe the skin layer formation and its dependence on the processing parameters, providing a mechanistic understanding of the photocrosslinking-induced phase separation under evaporative environments.

The quantum simulation setup of 87Rb Bose-Einstein condensates and numerical analysis of disorder induced dynamic-equilibrium localization

We report on a rapid production of 87Rb Bose-Einstein condensates(BECs) in a tight confinement hybrid trap based on single-beam optical dipole trap(ODT) and magnetic quadrupole trap(MQT). By the help of preliminary evaporation cooling in MQT, more atoms can be transferred to ODT. Then the BEC phase transition will be achieved by forced evaporation in ODT. This setup has good optical access for loading multiple optical lattices and laser speckle to quantum simulation.In theory, we numerically analyze the dynamic behavior of Bose-Einstein condensates in one-dimensional disordered potential before its completely losing spatial quantum coherence. We find that localization length can be remarkably affected by both the disorder statistics and the atom interaction. We also find that the phase of the condensates is broken into many small pieces while the system approaching localization, showing a counter-intuitive step-wise phase but not a thoroughly randomized phase. Although the condensates as a whole showing less flow and expansion, large currents occur where the phase changes abruptly. Thus we show explicitly that the localization of a finite size BEC is dynamic-equilibrium.

Techniques to cool and rotate Bose-Einstein condensates in time-averaged adiabatic potentials

We report two novel techniques for cooling and rotating Bose-Einstein condensates in a dilute rubidium vapor that highlight the control and versatility afforded over cold atom systems by time-averaged adiabatic potentials (TAAPs). The intrinsic loss channel of the TAAP has been successfully employed to evaporatively cool a sample of trapped atoms to quantum degeneracy. The speed and efficiency of this process compares well with that of conventional forced rf evaporation. In an independent experiment, we imparted angular momentum to a cloud of atoms forming a Bose-Einstein condensate by introducing a rotating elliptical deformation to the TAAP geometry. Triangular lattices of up to 60 vortices were created. All findings reported herein result from straightforward adjustments of the magnetic fields that give rise to the TAAP.

Alternative route to Bose-Einstein condensation of two-electron atoms

We present a novel route to Bose-Einstein condensation devised for two-electron atoms, which do not admit practicable cooling techniques based upon narrow intercombination lines. A dipole trap for $^{40}$Ca atoms in the singlet ground state is loaded from a moderately cold source of metastable triplet atoms via spatially and energetically selective optical pumping permitting four orders of magnitude increase of the phase space density. Further cooling to quantum degeneracy is achieved by forced evaporation optimized to minimize three-body losses. In a combined loading and evaporation cycle of less than three seconds we are able to condense 3000 atoms.

Strongly Dipolar Bose-Einstein Condensate of Dysprosium

We report the Bose-Einstein condensation (BEC) of the most magnetic element, dysprosium. The Dy BEC is the first for an open f-shell lanthanide (rare-earth) element and is produced via forced evaporation in a crossed optical dipole trap loaded by an unusual, blue-detuned and spin-polarized narrowline magneto-optical trap. Nearly pure condensates of 1.5 × 10(4) (164)Dy atoms form below T = 30 nK. We observe that stable BEC formation depends on the relative angle of a small polarizing magnetic field to the axis of the oblate trap, a property of trapped condensates only expected in the strongly dipolar regime. This regime was heretofore only attainable in Cr BECs via a Feshbach resonance accessed at a high-magnetic field.

Bose-Einstein condensation of 87Rb in a levitated crossed dipole trap

We report an apparatus and method capable of producing Bose-Einstein condensates (BECs) of ~1x10^6 87Rb atoms, and ultimately designed for sympathetic cooling of 133Cs and the creation of ultracold RbCs molecules. The method combines several elements: i) the large recapture of a magnetic quadrupole trap from a magneto-optical trap, ii) efficient forced RF evaporation in such a magnetic trap, iii) the gain in phase-space density obtained when loading the magnetically trapped atoms into a far red-detuned optical dipole trap and iv) efficient evaporation to BEC within the dipole trap. We demonstrate that the system is capable of sympathetically cooling the |F=1,m_F=-1> and |1,0> sublevels with |1,+1> atoms. Finally we discuss the applicability of the method to sympathetic cooling of 133Cs with 87Rb.

An Experimental Technique for Determining the Hydraulic Properties of Unsaturated Pyroclastic Soils

Abstract The experimental technique proposed in the paper was designed to rapidly and reliably determine both the water retention curve and the permeability function of undisturbed natural pyroclastic soil samples. The technique was developed in the framework of an experimental research project on mudflows in pyroclastic soils in the southern Italian region of Campania (Italy). Grain-size distribution and void ratio of the particular pyroclastic soils suggested investigation of the hydraulic behavior for matric suction values in the range between 0 and 100 kPa. Our experimental technique consisted of a sequence of testing phases to be conducted on a single undisturbed soil sample: A constant head permeation test, a forced evaporation test, and finally a drying test in a pressure plate apparatus. Interpretation of the experimental data was based on inverse modelling and allowed both water retention curves and permeability functions to be determined. The six parameters of the Mualem–van Genuchten model were adopted to describe the hydraulic behavior of the tested soils. Each testing phase supplied experimental data to be used in the interpretation procedure: The permeation phase provided a matching data point for the permeability function near saturation; the forced evaporation test was related to the hydraulic behavior for matric suction values ranging from a few kPa to less than 80–90 kPa (i.e., mini-tensiometer functioning range); and the drying steps in the pressure plate apparatus provided information about the retention properties for matric suction values up to 1 MPa. The results shown in the paper clearly confirm the goodness of the experimental design and the interpretation procedure.

Investigation of Electrohydrodynamically-Enhanced Convective Heat and Mass Transfer from Water Surface

Enhancement of forced flow evaporation rate by applying electric field (corona wind) has been experimentally evaluated in this study. Corona wind produced by a fine wire electrode which was charged with positive high DC voltage impinges to water surface and leads to evaporation enhancement by disturbing the saturated air layer over the water surface. The study was focused on the effects of corona wind velocity, electrode spacing and air flow velocity on the level of evaporation enhancement. Two sets of experiments, i.e., with and without electric field, have been conducted. Data obtained from the first experiment were used as reference for evaluation of evaporation enhancement at the presence of electric field. Applied voltages ranged from corona threshold voltage to spark over voltage at 1 kV increments. The results showed that corona wind has great enhancement effect on the water evaporation rate, but its effectiveness gradually diminishes by increasing air flow velocity. Maximum enhancement ratios were 7.3 and 3.6 for air velocities of 0.125 and 1.75 m/s, respectively. Finally two empirical correlations were obtained for prediction of electrohydrodynamic evaporation enhancement and its coefficient of thermal performance.

Forced heat loss from body surface reduces heat flow to body surface

Heat stress is commonly relieved by forced evaporation from body surfaces. The mode of heat stress relief by heat extraction from the periphery is not clear, although it reduces rectal temperature. Radiant surface temperature (Ts) of the right half of the body surface was examined by thermovision in 4 lactating Holstein cows (30kg of milk/d) during 7 repeated cycles of forced evaporation created by 30s of wetting followed by 4.5min of forced airflow. Wetting was performed by an array of sprinklers (0.76m3/h), and forced airflow (>3m/s velocity) over the right side of the body surface was produced by fans mounted at a height of 3m above the ground. Sprinkling wetted the hind legs, rump, and chest, but not the lower abdomen side, front legs, or neck. The animals were maintained in shade at an air temperature of 28°C and relative humidity of 47%. Coat thickness was 1 to 2mm, so Ts closely represented skin temperature. Mean Ts of 5×20cm areas on the upper and lower hind and front legs, rump, chest, abdomen side, and neck were obtained by converting to temperature their respective gray intensity in single frames obtained at 10-s intervals. Little change occurred in Ts during the first wetting (0.1±0.6°C), but it decreased rapidly thereafter (1.6±0.6°C in the fifth wetting). The Ts also decreased, to a smaller extent, in areas that remained dry (0.7±1.0°C). In all body sites, a plateau in Ts was reached by 2min after wetting. The difference between dry and wet areas in the first cooling cycle was approximately 1.2°C. The Ts of different body areas decreased during consecutive cooling cycles and reached a plateau by 3 cooling cycles in dry sites (front leg, neck, abdomen side), by 5 cooling cycles in the hind leg, and 7 cooling cycles in the rump and chest. The reduction in mean Ts produced by 7 cycles was 4.0 to 6.0°C in wetted areas and 1.6 to 3.7°C in sites that were not wetted. Initial rectal temperature was 38.9±0.1°C; it remained unchanged during first 5 cooling cycles, decreased by 0.1°C after 7 cooling cycles, and decreased to 38.4±0.06°C after 8 to 10 cooling cycles, with no additional subsequent decrease. The concomitant reduction in Ts in dry and wet areas suggests an immediate vasoconstrictor response associated with heat extraction and later development of a cooler body shell. The reduction in rectal temperature represents a response involving transfer of heat from the body core to the body shell. This response mode requires consideration in settings of heat stress relief.

Bose-Einstein Condensation of Alkaline Earth Atoms:Ca40

We have achieved Bose-Einstein condensation of ;{40}Ca, the first for an alkaline earth element. The influence of elastic and inelastic collisions associated with the large ground-state s-wave scattering length of ;{40}Ca was measured. From these findings, an optimized loading and cooling scheme was developed that allowed us to condense about 2 x 10;{4} atoms after laser cooling in a two-stage magneto-optical trap and subsequent forced evaporation in a crossed dipole trap within less than 3 s. The condensation of an alkaline earth element opens novel opportunities for precision measurements on the narrow intercombination lines as well as investigations of molecular states at the ;{1}S-;{3}P asymptotes.

Heat transfer and pressure drop characteristics of forced convective evaporation in horizontal tubes with coiled wire inserts

Heat transfer enhancement and pressure drop increasing during evaporation of R-134a due to the presence of coiled wire insert inside a horizontal evaporator was studied experimentally. The test evaporator was an electrically heated copper tube of 1200 mm length and 7.5 mm inside diameter. Helically wire coils with different wire diameters of 0.5, 0.7, 1.0 and 1.5 mm and different coil pitches of 5, 8, 10 and 13 mm were made and used in full length of the test evaporator. For each inserted tube and also the plain tube, several test runs were carried out with different mass velocities and heat fluxes. From analysis of acquired data, it was found that the coiled wire inserts enhance the heat transfer coefficient but with a higher penalty due to the increasing of pressure drop, in comparison to that for the plain flow. An empirical correlation has been developed to predict the heat transfer coefficient during evaporation inside a horizontal tube in the presence of a coiled wire insert.

Three-wire magnetic trap for direct forced evaporative cooling

We propose a simple three-wire-based magnetic trap potential for direct forced evaporative cooling of neutral atoms without using induced spin-flip technologies. We have devised a method for controlling the trap depth without sacrificing its frequencies by only varying wire currents and external magnetic fields. By having multiples of these wires on different levels integrated into an atom chip, it is possible to attain Bose-Einstein condensation without the conventional forced evaporation technique.

Accelerating evaporative cooling of atoms into Bose-Einstein condensation in optical traps

We demonstrate a simple scheme to achieve fast, accelerating (runaway) evaporative cooling of optically trapped atoms by tilting the optical potential with a magnetic field gradient. Runaway evaporation is possible in this trap geometry due to the weak dependence of vibration frequencies on trap depth, which preserves atomic density during the evaporation process. Using this scheme, we show that Bose-Einstein condensation with $\ensuremath{\sim}{10}^{5}$ cesium atoms can be realized in $2--4\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ of forced evaporation. The evaporation speed and energetics are consistent with the three-dimensional evaporation picture, despite the fact that atoms can only leave the trap in the direction of tilt.

Granular Structure of Self-Assembled PAA/PAH and PSS/PAH Nascent Films Imaged in situ by LC-AFM

Liquid cell atomic force microscopy (LC-AFM) is used to image self-assembled polyelectrolyte films eliminating any drying effects on the film structure. Weak/weak and strong/weak polyelectrolyte films are formed by the alternated deposition of poly(acrylic acid) [PAA]/poly(allylamine hydrochloride) [PAH], and poly(sodium 4-styrene sulfonate) [PSS]/PAH, respectively, forming a granular surface structure. Number and area of grains (GN, GA) are used to characterize the surface of these films during their build up process. We show that hydrophilic PAA increases GA and decreases GN, while these parameters follow an opposite behavior with PSS. In both cases, GA and GN always have a simple inverse relationship, and then grain surface coverage (GS=GNGA) is nearly constant and independent of polyelectrolyte nature and the substrates used here, but also in the published data as well. The drying of the weak/weak film was also imaged after natural and forced solvent evaporation, and the surface structure is strongly affected, although the GS values keep roughly the same value found for wet films. The set of these results indicates that GS may be considered as a constant parameter during the build-up for the self-nascent assembled polyelectrolytes. The granular structure is still maintained after glucose oxidase adsorption on these films with comparable GS values.

All-optical production ofL7iBose-Einstein condensation using Feshbach resonances

We show an all-optical method of making 7Li condensate using tunability of the scattering length in the proximity of a Feshbach resonance. We report the observation of two new Feshbach resonances on |F = 1;mF = 0> state. The narrow (broad) resonance of 7 G (34 G) width is detected at 831 +- 4 G (884 +4 -13 G). Position of the scattering length zero crossing between the resonances is found at 836 +- 4 G. The broad resonance is shown to be favorable for run away evaporation which we perform in a crossed-beam optical dipole trap. Starting directly form the phase space density of a magneto-optical trap we observe a Bose-Einstein condensation threshold in less than 3 s of forced evaporation.

Forced depression of leaf hydraulic conductance in situ: effects on the leaf gas exchange of forest trees

Summary Recent work on the hydraulic conductance of leaves suggests that maximum photosynthetic performance of a leaf is defined largely by its plumbing. Pursuing this idea, we tested how the diurnal course of gas exchange of trees in a dry tropical forest was affected by artificially depressing the hydraulic conductance of leaves (Kleaf). Individual leaves from four tropical tree species were exposed to a brief episode of forced evaporation by blowing warm air over leaves in situ. Despite humid soil and atmospheric conditions, this caused leaf water potential (Ψleaf) to fall sufficiently to induce a 50–74% drop in Kleaf. Two of the species sampled proved highly sensitive to artificially depressed Kleaf, leading to a marked and sustained decline in the instantaneous rate of CO2 uptake, stomatal conductance and transpiration. Leaves of these species showed a depression of hydraulic and photosynthetic capacity in response to the ‘blow‐dry’ treatment similar to that observed when major veins in the leaf were severed. By contrast, the other two species sampled were relatively insensitive to Kleaf manipulation; photosynthetic rates were indistinguishable from control (untreated) leaves 4 h after treatment. These insensitive species demonstrate a linear decline of Kleaf with Ψleaf, while Kleaf in the two sensitive species falls precipitously at a critical water deficit. We propose that a sigmoidal Kleaf vulnerability enables a high diurnal yield of CO2 at the cost of exposing leaves to the possibility of xylem cavitation. Linear Kleaf vulnerability leads to a relatively lower CO2 yield, while providing better protection against cavitation.

Trapping metastable chromium atoms in a crossed optical dipole trap

We report the fast accumulation of up to 1 million 52Cr metastable atoms in a mixed trap formed by the superposition of a quadrupolar magnetic trap and a strongly confining optical trap. The cloud is at a temperature of 100 μK with a peak density of 1018 atoms/m3, which is a promising starting point to reach quantum degeneracy by forced evaporation in an optical trap.