Optimizing water-reuse and increasing water-saving potentials by linking treated industrial and municipal wastewater for a sustainable urban development.

New industrial and urban developments in water-scarce regions are often inhibited by their high demand for water from natural resources. In addition, there often is a lack of water for purposes that contribute to an improved quality of life, such as urban green spaces. Therefore, the integrated industrial-urban water-reuse concept presents a strategy by linking and reusing treated industrial and municipal wastewater flows to increase urban water-reuse potentials. The concept of combining different reuse water flows, from wastewater treatment plants from industrial parks, aims at significantly increasing the water-saving potentials compared to a separate consideration of the industrial wastewater flows.

Achieving short high-quality gate-all-around structures for horizontal nanowire field-effect transistors.

We introduce a fabrication method for gate-all-around nanowire field-effect transistors. Single nanowires were aligned perpendicular to underlying bottom gates using a resist-trench alignment technique. Top gates were then defined aligned to the bottom gates to form gate-all-around structures. This approach overcomes significant limitations in minimal obtainable gate length and gate-length control in previous horizontal wrap-gated nanowire transistors that arise because the gate is defined by wet-etching. In the method presented here gate-length control is limited by the resolution of the electron-beam-lithography process. We demonstrate the versatility of our approach by fabricating a device with an independent bottom gate, top gate, and gate-all-around structure as well as a device with three independent gate-all-around structures with 300, 200, and 150 nm gate length. Our method enables us to achieve subthreshold swings as low as 38 mV dec-1 at 77 K for a 150 nm gate length.

Quantum Szilard Engine with Attractively Interacting Bosons.

We show that a quantum Szilard engine containing many bosons with attractive interactions enhances the conversion between information and work. Using an ab initio approach to the full quantum-mechanical many-body problem, we find that the average work output increases significantly for a larger number of bosons. The highest overshoot occurs at a finite temperature, demonstrating how thermal and quantum effects conspire to enhance the conversion between information and work. The predicted effects occur over a broad range of interaction strengths and temperatures.

InAs Nanowire Transistors with Multiple, Independent Wrap-Gate Segments.

We report a method for making horizontal wrap-gate nanowire transistors with up to four independently controllable wrap-gated segments. While the step up to two independent wrap-gates requires a major change in fabrication methodology, a key advantage to this new approach, and the horizontal orientation more generally, is that achieving more than two wrap-gate segments then requires no extra fabrication steps. This is in contrast to the vertical orientation, where a significant subset of the fabrication steps needs to be repeated for each additional gate. We show that cross-talk between adjacent wrap-gate segments is negligible despite separations less than 200 nm. We also demonstrate the ability to make multiple wrap-gate transistors on a single nanowire using the exact same process. The excellent scalability potential of horizontal wrap-gate nanowire transistors makes them highly favorable for the development of advanced nanowire devices and possible integration with vertical wrap-gate nanowire transistors in 3D nanowire network architectures.

Fully tunable, non-invasive thermal biasing of gated nanostructures suitable for low-temperature studies.

There is much recent interest in the thermoelectric (TE) characterization of single nanostructures at low temperatures, because such measurements yield information that is complementary to traditional conductance measurements, and because they may lead to novel paradigms for TE energy conversion. However, previously reported techniques for thermal biasing of nanostructures are difficult to use at low temperatures because of unintended global device heating, the lack of ability to continuously tune the thermal bias, or limited compatibility with gating techniques. By placing a heater directly on top of the electrical contact to a single InAs nanowire, we demonstrate fully tunable thermal biases of up to several tens of Kelvin, combined with negligible overall heating of the device, and with full functionality of a back gate, in the temperature range between 4 K and 300 K.

Time-resolved X-ray diffraction investigation of the modified phonon dispersion in InSb nanowires.

The modified phonon dispersion is of importance for understanding the origin of the reduced heat conductivity in nanowires. We have measured the phonon dispersion for 50 nm diameter InSb (111) nanowires using time-resolved X-ray diffraction. By comparing the sound speed of the bulk (3880 m/s) and that of a classical thin rod (3600 m/s) to our measurement (2880 m/s), we conclude that the origin of the reduced sound speed and thereby to the reduced heat conductivity is that the C44 elastic constant is reduced by 35% compared to the bulk material.

Control and understanding of kink formation in InAs-InP heterostructure nanowires.

Nanowire heterostructures are of special interest for band structure engineering due to an expanded range of defect-free material combinations. However, the higher degree of freedom in nanowire heterostructure growth comes at the expense of challenges related to nanowire-seed particle interactions, such as undesired composition, grading and kink formation. To better understand the mechanisms of kink formation in nanowires, we here present a detailed study of the dependence of heterostructure nanowire morphology on indium pressure, nanowire diameter, and nanowire density. We investigate InAs-InP-InAs heterostructure nanowires grown with chemical beam epitaxy, which is a material system that allows for very abrupt heterointerfaces. Our observations indicate that the critical parameter for kink formation is the availability of indium, and that the resulting morphology is also highly dependent on the length of the InP segment. It is shown that kinking is associated with the formation of an inclined facet at the interface between InP and InAs, which destabilizes the growth and leads to a change in growth direction. By careful tuning of the growth parameters, it is possible to entirely suppress the formation of this inclined facet and thereby kinking at the heterointerface. Our results also indicate the possibility of producing controllably kinked nanowires with a high yield.

The fabrication of dense and uniform InAs nanowire arrays.

Nanowires are important candidates for use in future electronics, photonics and thermoelectrics applications. We focus here in particular on nanowires for use in thermoelectric power generation and present a method of fabricating dense uniform InAs nanowire arrays amenable to future incorporation of advanced heterostructures that could further increase the thermoelectric performance of these nanowires. In these applications it will be important to have the nanowires densely packed in order to give an appreciable amount of power output. Here we present the fabrication of such dense arrays, using metal-particle seeded growth and chemical beam epitaxy, where the metal particles are defined by electron beam lithography, metal evaporation and lift-off. We evaluate the potential of chemical beam epitaxy for the growth of dense, freestanding InAs nanowire arrays and describe the process that enabled us to achieve areal packing densities of up to 19% with a variation of only a few per cent in nanowire diameter and height. We close by discussing how even higher areal packing densities can be achieved.

Self-propelled Leidenfrost droplets.

We report that liquids perform self-propelled motion when they are placed in contact with hot surfaces with asymmetric (ratchetlike) topology. The pumping effect is observed when the liquid is in the Leidenfrost regime (the film-boiling regime), for many liquids and over a wide temperature range. We propose that liquid motion is driven by a viscous force exerted by vapor flow between the solid and the liquid.

Experimental investigation of the breakdown of the Onsager-Casimir relations.

We use magnetoconductance fluctuation measurements of phase-coherent semiconductor billiards to quantify the contributions to the nonlinear electric conductance that are asymmetric under reversal of magnetic field. We find that the average asymmetric contribution is linear in magnetic field (for magnetic flux much larger than 1 flux quantum) and that its magnitude depends on billiard geometry. In addition, we find an unexpected asymmetry in the power spectrum of the magnetoconductance with respect to reversal of magnetic field and bias voltage.

Reversible thermoelectric nanomaterials.

Irreversible effects in thermoelectric materials limit their efficiency and economy for applications in power generation and refrigeration. While electron transport is unavoidably irreversible in bulk materials, here we derive conditions under which reversible diffusive electron transport can be achieved in nanostructured thermoelectric materials. We provide a fundamental thermodynamic explanation for why the optimum density of states in a thermoelectric material is a delta function and for why inhomogeneous doping and segmentation improve the thermoelectric figure of merit.

Symmetry of two-terminal nonlinear electric conduction.

The well-established symmetry relations for linear transport phenomena cannot, in general, be applied in the nonlinear regime. Here we propose a set of symmetry relations with respect to bias voltage and magnetic field for the nonlinear conductance of two-terminal electric conductors. We experimentally confirm these relations using phase-coherent, semiconductor quantum dots.

Reversible quantum brownian heat engines for electrons.

Brownian heat engines use local temperature gradients in asymmetric potentials to move particles against an external force. The energy efficiency of such machines is generally limited by irreversible heat flow carried by particles that make contact with different heat baths. Here we show that, by using a suitably chosen energy filter, electrons can be transferred reversibly between reservoirs that have different temperatures and electrochemical potentials. We apply this result to propose heat engines based on mesoscopic semiconductor ratchets, which can quasistatically operate arbitrarily close to Carnot efficiency.

Diffusion in tilted periodic potentials: Enhancement, universality, and scaling.

An exact analytical expression for the effective diffusion coefficient of an overdamped Brownian particle in a tilted periodic potential is derived for arbitrary potentials and arbitrary strengths of the thermal noise. Near the critical tilt (threshold of deterministic running solutions) a scaling behavior for weak thermal noise is revealed and various universality classes are identified. In comparison with the bare (potential-free) thermal diffusion, the effective diffusion coefficient in a critically tilted periodic potential may be, in principle, arbitrarily enhanced. For a realistic experimental setup, an enhancement by 14 orders of magnitude is predicted so that thermal diffusion should be observable on a macroscopic scale at room temperature.

Oral clearance and acid production of dairy products during interaction with sweet foods.

UNLABELLED: Oral clearance and acid production were observed in 30 volunteers following the ingestion of sharp cheddar cheese (CC) and in 9 volunteers following the ingestion of milk chocolate (MC) and low-fat yogurt, and then when MC was eaten immediately after CC (CC/MC) and when CC was eaten following MC (MC/CC). After each test food or food combination had been ingested the volunteers were monitored at five different tooth sites. At each site, using an absorbent paper point, 4 oral fluid samples were collected at 30 min intervals. The five paper points from each sampling occasion were pooled, extracted with 1 ml of water and analyzed qualitatively and quantitatively for both carbohydrates and organic acids using HPLC. Data obtained for each food was averaged and subjected to statistical evaluation. With the CC, glucose clearance was prolonged, due to intermediate lactose degradation into galactose and glucose. The quantity of lactic acid produced during the four intervals was monitored for each of the test foods and their combinations. RESULTS: CC, MC, CC/MC, MC/CC 30 min after ingestion: 1.64, 3.47, 4.68, 2.97; after 60 min: 1.30, 1.24, 1.28, 1.43; after 90 min: 1.58, 1.02, 0.76, 0.43; after 120 min: 1.27, 0.90, 0.70, 0.42 mmol lactic acid/l oral fluid, respectively. The average total amount of lactic acid obtained during the two hour test period was (highest) CC/MC > MC > CC > MC/CC (lowest). The lowest amount of intra-oral lactic acid was observed (Student's t test, p < 0.05) when cheddar cheese (CC) was eaten immediately after the milk chocolate (MC). CLINICAL SIGNIFICANCE: Consumption of cheese (cheddar), immediately after a sweet meal, significantly reduces (approx. 30%) the amount of lactic acid produced in the oral cavity, when compared to the amount of acid obtained from the sweet food alone.

Quantitation of catecholamines in inflamed human dental pulp by high-performance liquid chromatography.

Catecholamines may play an important role in the control of intrapulpal pressure as mediators of vasoconstriction. A baseline level of catecholamines (dopamine, epinephrine, and norepinephrine) in the uninflamed human dental pulp was previously reported using high-performance liquid chromatography. The purpose of this study was to compare the level of catecholamines present in the inflamed human dental pulp with the baseline level established in virgin teeth. Twelve uninflamed pulps were analyzed as a control and to validate previous findings. Pulp tissue was obtained from 10 vital and inflamed teeth requiring endodontic treatment. Selective criteria for each patient included: absence of systemic disease, medications, and allergies; a vital response to ice, heat, and electric pulp tests; and periodontal probing < or = 3 mm. A prior history of pain associated with the tooth was an additional criterion for inflamed pulps. To avoid the presence of an exogenous catecholamine, local anesthesia without epinephrine was administered. Dopamine, epinephrine, and norepinephrine were chemically extracted and analyzed by high-performance liquid chromatography with ultraviolet detection. Catecholamine levels found to be present in the pulp during inflammation were greater than the baseline level established in uninflamed pulp tissue.

Giant acceleration of free diffusion by use of tilted periodic potentials.

The effective diffusion coefficient for the overdamped Brownian motion in a tilted periodic potential is calculated in closed analytical form. Universality classes and scaling properties for weak thermal noise are identified near the threshold tilt where deterministic running solutions set in. In this regime the diffusion may be greatly enhanced, as compared to free thermal diffusion with, for a realistic experimental setup, an enhancement of up to 14 orders of magnitude.

Evolution of fractal patterns during a classical-quantum transition.

We investigate how fractals evolve into nonfractal behavior as the generation process is gradually suppressed. Fractals observed in the conductance of semiconductor billiards are of particular interest because the generation process is semiclassical and can be suppressed by transitions towards either fully classical or fully quantum-mechanical conduction. Investigating a range of billiards, we identify a "universal" behavior in the changeover from fractal to nonfractal conductance, which is described by a smooth evolution rather than deterioration in the fractal scaling properties.

Effect of increasing sucrose concentrations on oral lactic acid production.

UNLABELLED: Oral lactic acid production was studied on 11 healthy dental student volunteers (5 males and 6 females) during clearance of five solutions containing 5, 10, 15, 20 and 30% of sucrose. Oral fluid samples were collected at times zero, immediately before taking the sucrose solutions ('baseline'), and 15 min following intake of the solutions. The samples were analyzed qualitatively and quantitatively for the presence of lactic acid and remaining sugars using high-performance liquid chromatography (HPLC). Results indicate that the amount of lactic acid in oral fluid significantly increased with increasing sucrose concentrations, up to 15% sucrose. With the higher sucrose concentrations (20 and 30%) equivalent or lower amounts of lactic acid were obtained. The threshold level for maximum lactic acid production was found to be between 10 and 15% sucrose. Statistical analysis of the data (Student's t test) indicated a significant difference in lactic acid production between the 5 and 10% sucrose solutions versus the 15, 20 and 30% sucrose solutions tested (p < 0.05). CLINICAL SIGNIFICANCE: Ingestion of solutions with higher sucrose concentrations (>15%) produced similar amounts or less of lactic acid during oral clearance than solutions containing lower sucrose concentrations (<15%).

Experimental tunneling ratchets

Adiabatically rocked electron ratchets, defined by quantum confinement in semiconductor heterostructures, were experimentally studied in a regime where tunneling contributed to the particle flow. The rocking-induced electron flow reverses direction as a function of temperature. This result confirms a recent prediction of fundamentally different behavior of classical versus quantum ratchets. A wave-mechanical model reproduced the temperature-induced current reversal and provides an intuitive explanation.