Shallow Potential Research Articles

Stacking-sequence-independent band structure and shear exfoliation of two-dimensional electride materials

The electronic band structure of crystals is generally influenced by the periodic arrangement of their constituent atoms. Specifically, the emerging two-dimensional (2D) layered structures have shown different band structures with respect to their stacking configurations. Here, based on first-principles density-functional theory calculations, we demonstrate that the band structure of the recently synthesized 2D Ca$_2$N electride changes little for the stacking sequence as well as the lateral interlayer shift. This intriguing invariance of band structure with respect to geometrical variations can be attributed to a complete screening of [Ca$_2$N]$^{+}$ cationic layers by anionic excess electrons delocalized between the cationic layers. The resulting weak interactions between 2D dressed cationic layers give rise to not only a shallow potential barrier for bilayer sliding but also an electron-doping facilitated shear exfoliation. Our findings open a route for exploration of the peculiar geometry-insensitive electronic properties in 2D electride materials, which will be useful for future thermally stable electronic applications.

Relaxing the cosmological constant: a proof of concept

We propose a technically natural scenario whereby an initially large cosmological constant (c.c.) is relaxed down to the observed value due to the dynamics of a scalar evolving on a very shallow potential. The model crucially relies on a sector that violates the null energy condition (NEC) and gets activated only when the Hubble rate becomes sufficiently small --- of the order of the present one. As a result of NEC violation, this low-energy universe evolves into inflation, followed by reheating and the standard Big Bang cosmology. The symmetries of the theory force the c.c. to be the same before and after the NEC-violating phase, so that a late-time observer sees an effective c.c. of the correct magnitude. Importantly, our model allows neither for eternal inflation nor for a set of possible values of dark energy, the latter fixed by the parameters of the theory.

A pump/leak model of growth: the biophysics of cell elongation in higher plants revisited.

Current concepts of growth hydraulics in higher plants are critically revisited, and it is concluded that they partly fail to interpret the experimental data adequately, particularly in the case of hydroponics-grown roots. Theoretical considerations indicate that the growth rate in roots is controlled by the extensibility of the cell wall, excluding water availability (i.e. hydraulic conductance) as a major constraint. This is supported by the findings that the growth rate does not scale with turgor, and that no radial nor axial water potential gradients have been observed in the root elongation zone. Nevertheless, a water potential deficit ranging from -0.2 to -0.6MPa has repeatedly been reported for growing cells that by far exceeds the shallow trans-membrane water potential difference required for the uptake of growth water. Unexpectedly, growth was also shown to depend on the hydraulic conductance (LP) of the plasma membrane of root cells, even though LP should generally be too large to have an impact on growth. For leaves, similar observations have been reported, but the interpretation of the data is less straightforward. Inconsistencies associated with the current model of growth hydraulics prompt the author to suggest a revised model that comprises, in addition to a passive mechanism of water transport across the plasma membrane of growing cells mediated by aquaporins ('leak') a secondary active water transport ('pump'), in analogy to a mechanism previously demonstrated for mammalian epithelia and postulated for xylem parenchyma cells in roots. Water is hypothesised to be secreted against a trans-membrane water potential difference by cotransport with solutes (salts, sugars, and/or amino acids), taking advantage of the free energy released by this transport step. The solute concentration gradient is supposed to be maintained by a subsequent retrieval of the solutes from the apoplast and back-transport at the expense of metabolic energy. Water secretion tends to reduce the turgor pressure and retards growth, but turgor and, in turn, growth can be upregulated very rapidly independent from any adjustment in the osmolyte deposition rate by increasing LP and/or reducing secondary active water transport, e.g. when the root is exposed to mild osmotic stress, as confirmed by experimental studies.

Assessment and mapping of the shallow geothermal potential in the province of Cuneo (Piedmont, NW Italy)

Ground Source Heat Pump (GSHP) is a low carbon heating and cooling technology which can make an important contribution for reaching the ambitious CO2 reduction targets set by the European Union. The economic and technical suitability of this technology strongly depends on the thermal and hydrogeological properties of the ground at the installation site, which need to be assessed in detail. A common indicator adopted to define such suitability is the geothermal potential, i.e. the thermal power that can be exchanged with the ground through a GSHP with a certain setup. In this paper, we present the assessment and mapping of the shallow geothermal potential in the province of Cuneo, a 6900 km2 wide county in NW Italy. Geological, hydrogeological and climatic information are collected and processed to estimate the relevant ground properties. The shallow geothermal potential is then estimated with different methods for closed-loop installations (Borehole Heat Exchangers, BHEs) and open-loop installations (Ground Water Heat Pumps, GWHPs) systems in order to identify the most suitable areas for different technologies. The maps of the geothermal potential are an important planning tool for the installation of GSHPs and for the growth of this renewable energy source.

Quantification of exploitable shallow geothermal energy by using Borehole Heat Exchanger coupled Ground Source Heat Pump systems

In previous studies, the amount of exploitable shallow geothermal energy was estimated by assuming a uniform temperature drop of 2–6°C in the aquifer. In this work, a more comprehensive numerical model has been employed to evaluate the available amount of shallow geothermal energy by using Borehole Heat Exchanger coupled Ground Source Heat Pump systems. Numerical experiments have been performed by simulating the long-term evolution of the subsurface temperature field, which is subject to the operation of borehole heat exchangers and varying parameters like subsurface thermal conductivity and groundwater flow velocity. The concept of equivalent temperature drop is proposed as an auxiliary quantity for the subsurface. With the help of this parameter, a procedure has been established to quantify the amount of shallow geothermal potential. Following this approach, a realistic equivalent temperature reduction is found to be from −1.8 to −4.4°C in the subsurface over a period of 30years. This can be translated to an annual extractable geothermal energy value in a unit surface area, and it ranges from 3.5 to 8.6kWhm−2a−1. The exact value is site specific and heavily depends on the soil thermal conductivity, groundwater velocity, and borehole arrangement.

Goldilocks models of higher-dimensional inflation (including modulus stabilization)

We explore the mechanics of inflation within simplified extra-dimensional models involving an inflaton interacting with the Einstein-Maxwell system in two extra dimensions. The models are Goldilocks-like inasmuch as they are just complicated enough to include a mechanism to stabilize the extra-dimensional size (or modulus), yet simple enough to solve explicitly the full extra-dimensional field equations using only simple tools. The solutions are not restricted to the effective 4D regime with H ≪ mKK (the latter referring to the characteristic mass splitting of the Kaluza-Klein excitations) because the full extra-dimensional Einstein equations are solved. This allows an exploration of inflationary physics in a controlled calculational regime away from the usual four-dimensional lamp-post. The inclusion of modulus stabilization is important because experience with string models teaches that this is usually what makes models fail: stabilization energies easily dominate the shallow potentials required by slow roll and so open up directions to evolve that are steeper than those of the putative inflationary direction. We explore (numerically and analytically) three representative kinds of inflationary scenarios within this simple setup. In one the radion is trapped in an inflaton-dependent local minimum whose non-zero energy drives inflation. Inflation ends as this energy relaxes to zero when the inflaton finds its own minimum. The other two involve power-law scaling solutions during inflation. One of these is a dynamical attractor whose features are relatively insensitive to initial conditions but whose slow-roll parameters cannot be arbitrarily small; the other is not an attractor but can roll much more slowly, until eventually transitioning to the attractor. The scaling solutions can satisfy H > mKK, but when they do standard 4D fluctuation calculations need not apply. When in a 4D regime the solutions predict η ≃ 0 and so r ≃ 0.11 when ns ≃ 0.96 and so are ruled out if tensor modes remain unseen. Assessment of general parameters is difficult until a full 6D fluctuation calculation is done.

Bimodal momentum distribution of laser-cooled atoms in optical lattices

We study, numerically and experimentally, the momentum distribution of atoms cooled in optical lattices. Using semi-classical simulations, we show that this distribution is bimodal, made up of a central feature corresponding to "cold", trapped atoms, with tails of "hot", untrapped atoms, and that this holds true also for very shallow potentials. Careful analysis of the distribution of high-momentum untrapped atoms, both from simulations and experiments, shows that the tails of the distribution does not follow a normal law, hinting at a power-law distribution and non-ergodic behavior. We also revisit the phenomenon of d\'ecrochage, the potential depth below which the temperature of the atoms starts increasing.

G.POT: A quantitative method for the assessment and mapping of the shallow geothermal potential

GSHPs (Ground source heat pumps) exchange heat with the ground to provide sustainable heating or cooling. Their technological feasibility and economic viability depend on the site-specific thermal properties of the ground and on the usage profile of the plant. These parameters influence the shallow geothermal potential, which is defined as the thermal power that can be efficiently exchanged by a BHE (Borehole Heat Exchanger) of a certain depth. We present a general method (G.POT) for the determination of shallow geothermal potentials. This method was derived using a comprehensive set of analytical heat transfer simulations, performed by varying (i) the thermal properties of the ground, which comprise its thermal conductivity and capacity, (ii) the thermal properties of the borehole, and (iii) the operational and design parameters of the plant, namely, the BHE length, the threshold temperature of the heat carrier fluid, the duration of the heating/cooling season and the simulated lifetime. Therefore, the G.POT method is a simple and flexible tool that can be implemented in a wide range of different scenarios for large-scale mapping of geothermal potentials. We also assess G.POT by discussing its application to map the geothermal yield in the Province of Cuneo (Piemonte, NW Italy).

The waterfall paradox: How knickpoints disconnect hillslope and channel processes, isolating salmonid populations in ideal habitats

Waterfalls create barriers to fish migration, yet hundreds of isolated salmonid populations exist above barriers and have persisted for thousands of years in steep mountainous terrain. Ecological theory indicates that small isolated populations in disturbance-prone landscapes are at greatest risk of extirpation because immigration and recolonization are not possible. On the contrary, many above-barrier populations are currently thriving while their downstream counterparts are dwindling. This quandary led us to explore geomorphic knickpoints as a mechanism for disconnecting hillslope and channel processes by limiting channel incision and decreasing the pace of base-level lowering. Using LiDAR from the Oregon Coast Range, we found gentler channel gradients, wider valleys, lower gradient hillslopes, and less shallow landslide potential in an above-barrier catchment compared to a neighboring catchment devoid of persistent knickpoints. Based on this unique geomorphic template, above-barrier channel networks are less prone to debris flows and other episodic sediment fluxes. These above-barrier catchments also have greater resiliency to flooding, owing to wider valleys with greater floodplain connectivity. Habitat preference models further indicate that salmonid habitat is present in greater quantity and quality in these above-barrier networks. Therefore the paradox of the persistence of small isolated fish populations may be facilitated by a geomorphic mechanism that both limits their connectivity to larger fish populations yet dampens the effect of disturbance by decreasing connections between hillslope and channel processes above geomorphic knickpoints.

Use rights markets for shallow geothermal energy management

Due to the growth in demand for shallow geothermal energy, the development of an integrated management system to organize the exploitation of this resource is mandatory to protect both groundwater and the users’ rights. This paper proposes a methodology to establish a market of shallow geothermal energy use rights which will represent an advance in the management of this resource. The new concept developed to define the basic unit of management is the thermal plot. It is related to the shallow geothermal potential of a registered plot of land. This methodology is based on a GIS framework (ArcGIS, ESRI) and is composed of a geospatial database (Personal Geodatabase, ESRI) to store the main information required to manage the SGE systems, such as groundwater velocity, thermal conductivity or thermal heat capacity, and a set of GIS tools used to define, implement and control this use rights market. The exchanged heat rate and thermal disturbance are calculated on the basis of analytical solutions of heat transport equation in porous media. Thermal impacts derived from the exploitation of this resource can also be registered geographically, by taking into account the groundwater flow direction and adjusting the thermal impact to the available plot. A synthetic application of this methodology is presented for the Metropolitan Area of Barcelona, Spain.

THE INNER STRUCTURE OF DWARF-SIZED HALOS IN WARM AND COLD DARK MATTER COSMOLOGIES

ABSTRACT By means of N-body + hydrodynamic zoom-in simulations we study the evolution of the inner dark matter and stellar mass distributions of central dwarf galaxies formed in halos of virial masses M v = (2–3) × 1010 h −1 M ⊙ at z = 0, both in a warm dark matter (WDM) and cold dark matter (CDM) cosmology. The half-mode mass in the WDM power spectrum of our simulations is M f = 2 × 1010 h −1 M ⊙. In the dark matter (DM) only simulations halo density profiles are well described by the Navarro–Frenk–White parametric fit in both cosmologies, though the WDM halos have concentrations lower by factors of 1.5–2.0 than their CDM counterparts. In the hydrodynamic simulations, the effects of baryons significantly flatten the inner density, velocity dispersion, and pseudo phase space density profiles of the WDM halos but not of the CDM ones. The density slope, measured at ≈0.02R v, α 0.02, becomes shallow in periods of 2–5 Gyr in the WDM runs. We explore whether this flattening process correlates with the global star formation (SF), M s/M v ratio, gas outflow, and internal specific angular momentum histories. We do not find any clear trends, but when α 0.02 is shallower than −0.5, M s/M v is always between 0.25% and 1%. We conclude that the main reason for the formation of the shallow core is the presence of strong gas mass fluctuations inside the inner halo, which are a consequence of the feedback driven by a very bursty and sustained SF history in shallow gravitational potentials. Our WDM halos, which assemble late and are less concentrated than the CDM ones, obey these conditions. There are also (rare) CDM systems with extended mass assembly histories that obey these conditions and form shallow cores. The dynamical heating and expansion processes behind the DM core flattening apply also to the stars in such a way that the stellar age and metallicity gradients of the dwarfs are softened, their stellar half-mass radii strongly grow with time, and their central surface densities decrease.

Investigating environmental trends in the outer visible edges of dwarf irregular galaxies

AbstractThe star formation histories and evolution of 28 dwarf irregular galaxies (dIs) that reside in differing local and global environments are investigated. The shallow gravitational potentials of dwarf galaxies make these objects highly susceptible to changes in morphology or dynamics by external perturbations. Additionally, the lack of more complicated structures such as spiral arms makes environmental effects more easily discernible. Therefore, dIs are ideal candidates for a study of the role of environment in galaxy evolution. The local environment is defined by the local galaxy number density, where high indicates at least one neighbor within 200 kpc and low indicates no neighbors within 1 Mpc. The global environment is classified as either the field or a galaxy group / cluster.Absolute magnitudes, colors, central surface brightnesses, star formation rates and color profiles were compared using photometry from UBVR and Hα imaging. While some environmental trends are noted (galaxies in local high density environments have brighter central and effective surface brightnesses, while those in global high density environments have brighter absolute magnitudes, central and effective surface brightnesses, and higher star formation rates), no systematic environmental trends are seen in the shape of the color profiles or spatial distribution of recent star formation. A lack of environmental trend in star formation and galaxy color indicates that either internal processes dominate the formation and subsequent evolution of the outskirts of dIs, or there is no systematic environmental effect on such. The appearance of environmental effects should be more noticeable at the outermost edges of these systems. The lack of a trend in such implies that the exact nature of the environmental influence varies greatly depending on the exact nature of the interaction occurring.

Comparison of different methods for ground thermal properties determination in a clastic sedimentary environment

Energy Strategy of the Republic of Croatia by 2020 relies on renewable energy resources as one of the main priorities. The use of geothermal energy sources is specifically encouraged. Within the research project “Research and the Promotion of the Use of Shallow Geothermal Potential in Croatia”, an improved method, the so called distributed thermal response test (DTRT) has been applied on a 100m deep borehole heat exchanger (double U pipe) within a borehole of 152mm outer diameter. The fundamental difference from the thermal response test (TRT) is the measurement of the carrier fluid temperature along the borehole heat exchanger (BHE) using an optic fiber cable placed inside the BHE pipes. Hence, in DTRT vertical distribution of the ground thermal conductivity and borehole thermal resistance are determined along the borehole heat exchanger. The undisturbed ground temperature profile along the BHE was also determined using this method. The work presented in this paper shows measurements from the borehole heat exchanger installation located in the city of Osijek, and determination of the ground thermal conductivity for specific geological settings using three different approaches: DTRT, TRT and direct measurement of sediment thermal properties. In a fluvial sedimentary sequence found in Osijek the discrepancy of DTRT and TRT results are 3.65% for thermal conductivity and 2.25% for borehole thermal resistance, while comparison of weighted averaged ground thermal conductivity results of DTRT and the direct thermal measurement yielded difference of 8.74%.

Mott transition for strongly interacting one-dimensional bosons in a shallow periodic potential

We investigate the superfluid-insulator transition of one-dimensional interacting Bosons in both deep and shallow periodic potentials. We compare a theoretical analysis based on Monte-Carlo simulations in continuum space and Luttinger liquid approach with experiments on ultracold atoms with tunable interactions and optical lattice depth. Experiments and theory are in excellent agreement. It provides a quantitative determination of the critical parameter for the Mott transition and defines the regime of validity of widely used approximate models, namely the Bose-Hubbard and sine-Gordon models

GIS-based modelling of shallow geothermal energy potential for CO2 emission mitigation in urban areas

Due to the rapidly increasing percentage of the population living in urban centres, there is a need to focus on the energy demand of these cities and the use of renewable energies instead of fossil fuels. In this paper, we develop a spatial model to determine the potential per parcel for using shallow geothermal energy, for space heating and hot water. The method is based on the space heating and hot water energy demand of each building and the specific heat extraction potential of the subsurface per parcel. With this information, along with the available space per parcel for boreholes, the percentage of the energy demand that could be supplied by geothermal energy is calculated. The potential reduction in CO2 emissions should all possible geothermal energy be utilised, is also calculated. The method is applied to Ludwigsburg, Germany. It was found that CO2 emissions could potentially be reduced by 29.7% if all space heating and hot water requirements were provided by geothermal energy, which would contribute to the sustainability of a city. The method is simple in execution and could be applied to other cities as the data used should be readily available. Another advantage is the implementation into the web based Smart City Energy platform which allows interactive exploration of solutions across the city.

Dynamical symmetry and pair tunneling in a one-dimensional Bose gas colliding with a mobile impurity

Using the time-dependent density matrix renormalization group (TDMRG) we theoretically study the collision of a one-dimensional gas of interacting bosons with an impurity trapped in a shallow box potential. We study the dynamic response of both the impurity and the bosonic gas and find an approximate independence of the sign of the interaction (attractive or repulsive) between the impurity and the bosons. This sign-independence breaks down when the interaction energy is of the same order as the box potential depth, leading to resonant pair tunneling. Our predictions can be tested using contemporary techniques with ultracold atoms.

Metallicity Gradients in the Halos of Elliptical Galaxies

AbstractWe discuss the stellar halos of massive elliptical galaxies, as revealed by our ambitious integral-field spectroscopic survey MASSIVE. We show that metallicity drops smoothly as a function of radius out to ~ 2.5 Re, while the [α/Fe] abundance ratios stay flat. The stars in the outskirts likely formed rapidly (to explain the high ratio of alpha to Fe) but in a relatively shallow potential (to explain the low metallicities). This is consistent with expectations for a two-phase growth of massive galaxies, in which the second phase involves accretion of small satellites. We also show some preliminary study of the gas content of these most MASSIVE galaxies.

Electromagnetic and DC methods for geothermal exploration in Italy – case studies and future developments

Geothermal energy is a renewable and eco-compatible resource suitable for base-load power and thermal production, which means a daily continuous energy production. In the past few years this source has been of interest for governments, companies and research institutes worldwide that are working for the increase of geothermal exploitation with the aim of reducing greenhouse gas emissions and fossil fuels consumption. Italy was the first country (in 1913) where geothermal energy was exploited for industrial power production and is now the sixth-largest geothermal electricity producer in the world (Bertani, 2015). The geothermal potential of Italy, both for power production and direct uses, is really huge due to particular geological conditions; elsewhere it is mostly underexploited for non-technical barriers. In Italy, many industrial and scientific exploration pro¬jects have been carried out in the last few years for assessing shallow and deep geothermal resources. ElectroMagnetic (EM) methods play a fundamental role in the geothermal exploration due to particular sensitivity of the subsurface electrical resistivity (hereby resistivity) to hydro¬thermal circulation, thermal regime and rocks alteration. Many papers have been published on the study of geothermal areas by EM methods worldwide (Meju, 2002; Spichak and Manzella, 2009; Muñoz, 2014 and references therein). In this paper, we propose an updated state-of-the-art of the main electromagnetic and direct current methods for geother¬mal exploration in Italy, describing innovative case studies and including a discussion about the direction of new researches. The Magnetotellurics (MT) represents the most common and effective method for investigating deep geothermal res¬ervoirs. A case study in southern Tuscany is herein described. We will also focus the attention on the resistivity measure¬ments for shallow geothermal exploration by means of Airborne EM (AEM), Transient or Time Domain EM (TEM or TDEM) and Electrical Resistivity Tomography (ERT). Among the various scientific projects for geothermal exploration that the Italian National Research Council (CNR) carried out, the VIGOR project (evaluation of the geothermal potential of Regions of Convergence) for Southern Italy provided the occasion of detailed geoelectro¬magnetic studies for assessing shallow and deep geothermal resources (Manzella et al. 2013a, VIGOR website). Some cases study of the VIGOR project are briefly described as: i) the innovative application of Airborne EM data acquired over large areas in Sicily and applied to the assessment of shallow geothermal potential and ii) a Deep Electrical Resistivity Tomography (DERT) acquired on a thermal area in Calabria region.

Interaction-Driven Topological Insulator in Fermionic Cold Atoms on an Optical Lattice: A Design with a Density Functional Formalism.

We design an interaction-driven topological insulator for fermionic cold atoms in an optical lattice; that is, we pose the question of whether we can realize in a continuous space a spontaneous symmetry breaking induced by the interatom interaction into a topological Chern insulator. Such a state, sometimes called a "topological Mott insulator," has yet to be realized in solid-state systems, since this requires, in the tight-binding model, large off-site interactions on top of a small on-site interaction. Here, we overcome the difficulty by introducing a spin-dependent potential, where a spin-selective occupation of fermions in A and B sublattices makes the on-site interaction Pauli forbidden, while a sizeable intersite interaction is achieved by a shallow optical potential with a large overlap between neighboring Wannier orbitals. This puts the system away from the tight-binding model, so that we adopt density functional theory for cold atoms, here extended to accommodate noncollinear spin structures emerging in the topological regime, to quantitatively demonstrate the phase transition to the topological Mott insulator.

Water Contamination, Land Prices, and the Statute of Repose

We examine how water contamination risk from an inactive hazardous waste site is capitalized into surrounding vacant land prices. After public knowledge of the first instance of off-site contamination, we find that shallow groundwater contamination potential is negatively capitalized into land prices, as is proximity to a known contaminated well. Public knowledge of off-site contamination and associated land price changes occur after the North Carolina’s 10-year statue of repose. Our findings raise questions concerning such statutes when environmental contamination has a long latency period, especially given a recent Supreme Court ruling that Superfund law does not preempt state statutes of repose.