Deep Potential Well Research Articles

The Ionized Gas in Local Starburst Galaxies: Global and Small-Scale Feedback from Star Formation

Abridged: The small-- and intermediate--scale structure and the fraction of the ISM ionized by non--radiative processes is investigated in a small sample of four local starburst galaxies, imaged with the HST WFPC2. The sample comprises three dwarf galaxies, NGC3077, NGC4214, and NGC5253, and one giant spiral, NGC5236 (M83). The galaxies span a range in metallicity, luminosity, and environment, enabling the investigation of non--radiative ionization processes in a variety of galactic conditions. For this purpose, the four galaxies were imaged in the lines of H-beta(4861 A), [OIII](5007 A), H-alpha(6563 A), and [SII](6717,6731 A). The non--photoionized gas in these galaxies has been traced on scales ranging from a few tens of pc to a few hundred pc, providing a full budget for this ionized gas component. Using the `maximum starburst line' of Kewley et al. (2001) to discriminate between photoionized and non--photoionized gas, we find that in all four galaxies non--photoionization processes are responsible for a small fraction of the total H-alpha emission, at the level of 3%--4%. The starbursts in the three dwarf galaxies deposit a significant fraction, 70%-100%, of their mechanical energy into the surrounding interstellar medium and require time--extended (a few x 10^7 yr to ~10^8 yr) star formation, in order to account for the observed luminosity of the non--photoionized gas. In the massive spiral, the non--photoionized gas is concentrated in localized areas surrounded by active star--formation, with no evidence for extended structures (as those in the dwarfs). This confirms the picture that starbursts remain confined events in massive galaxies, likely due to the deep potential well.

Theoretical Analysis of Diamond Mechanosynthesis. Part I. Stability of C<SUB>2</SUB> Mediated Growth of Nanocrystalline Diamond C(110) Surface

A theoretical investigation of the chemical vapor deposition (CVD) growth on clean diamond C(110) surfaces from carbon dimer precursors shows that isolated deposited C2 dimers appear stable at room temperature, but a second carbon dimer subsequently chemisorbed in close vicinity to the first can adopt one of 19 local energy minima, five of which require barriers � 0.5 eV to reach the global minimum and, thus, constitute stabilized defects. Three chemisorbed C2 dimers can adopt one of 35 local minimum energy structures, 10 of which are stable defects located in deep potential energy wells. The number of potential defects increases with the number of deposited carbon dimers, which suggests an isolated rather than clustered growth mechanism in CVD on bare diamond C(110). These results also provide information regarding outcomes of the misplacement of a carbon dimer and establish constraints on the required dimerplacement positional precision that would be needed to avoid the formation of stable defects during diamond surface growth.

Investigation of theα-cluster structure ofNe22andMg22

An excitation function for resonance elastic scattering of α particles on O18 and Ne18 was measured using the method of inverse geometry with a very thick target. Spectroscopic information was obtained for 23 levels in the excitation energy region from 11.9 to 13.7MeV in Ne22. Twelve of them are new. General features of α-cluster bands in Ne22 are analyzed in the framework of the potential model with a deep potential well. Predictions for the 11− level in Ne22, as well as for the isotopic shift of the cluster levels in Mg22, are given. Evidence is presented that new perspectives on the study of nuclear structure and nuclear spectroscopy can be obtained in complimentary measurements of α-cluster states in mirror N≠Z nuclei.3 MoreReceived 10 July 2003DOI:https://doi.org/10.1103/PhysRevC.69.024602©2004 American Physical Society

Theoretical Study of the Reaction Mechanism of BO, B2O2, and BS with H2

Potential energy surfaces of various reactions in the BO/H 2 , B 2 O 2 /H 2 , and BS/H 2 systems have been studied at the G2M(MP2)//B3LYP/6-311+G(d,p) level of theory. The BO + H 2 reaction is shown to proceed by ion of a hydrogen atom by B to produce OBH + H with the barrier and exothermicity of 8.3 and 6.8 kcal/mol, respectively. The reaction can also occur by 1,2-insertion of BO into the H-H bond or by H ion by the O atom; however, the barriers for these channels are much higher, 36.4 and 42.7 kcal/mol, respectively. Via a low ∼0.3 kcal/mol barrier, the OBH + H reaction produces the OBH 2 radical, which is the most stable compound in the BO/H 2 system and lies 15.9, 2.5, and 4.2 kcal/mol below BO + H 2 , trans-HBOH, and cis-HBOH, respectively. OBH 2 can isomerize to trans-HBOH overcoming a barrier of 27.7 kcal/ mol and the latter can rearrange to the cis conformer with a barrier of 10.8 kcal/mol. BOH and H can recombine and form cis- or trans-HBOH without barriers. In the B + H 2 O reaction, the reactants can first form a weakly bound B-H 2 O complex, which then can eliminate an H atom producing BOH + H or undergo insertion of B into an O-H bond giving trans-HBOH with barriers of 4.7 and 6.2 kcal/mol relative to the initial reactants, respectively, and trans-HBOH can eventually decompose to OBH + H and a minor amount of BO + H 2 . Singlet OBBO is shown to be much less reactive with respect to H 2 than the BO monomer. Alternatively, after two BO recombine to form a triplet OBBO molecule over a moderate 8.3 kcal/mol barrier, t-OBBO can easily react with H 2 producing either BO + OBH 2 (via a t-OBBH 2 O intermediate) or OBBOH + H with barriers of 4.4 and 7.4 kcal/mol, respectively. The reactions in the BS/H 2 system are shown to be similar to those for BO/H 2 , except that BS cannot insert into H 2 , SBH 2 resides in a much deeper potential well (37.3 kcal/mol below BS + H 2 ) and can rearrange both to trans- and cis-HBSH, the B-H 2 S complex is more strongly bound than B-H 2 O, and the B + H 2 S reaction is expected to be significantly faster than the reaction of B + H 2 O.

Decay‐rate dependence of anhysteretic remanence: Fundamental origin and paleomagnetic applications

We have measured the intensity of anhysteretic remanent magnetization (ARM) as a function of alternating field (AF) decay rate. For synthetic and natural single‐domain (SD) and pseudo‐single‐domain (PSD) magnetites, ARM intensity increases as decay rate decreases. Multidomain (MD) magnetites have the opposite response, ARM increasing as the decay rate increases. These are identical to the SD/PSD and MD dependences of thermoremanent magnetization on cooling rate. For all grain sizes and domain structures, ARM intensity increases as the AF decay rate used to achieve an initial demagnetized state decreases. Decay‐rate differences in ARM intensity are a property of low‐ and medium‐coercivity grains, as shown by annealing and by stepwise AF demagnetizing samples. We interpret the SD results to mean that increased AF exposure time permits a closer approach to equilibrium magnetization. An approximate thermal activation theory based on Néel [1949] and an exact theory by Egli and Lowrie [2002] predict 6–11% increases in ARM for an order of magnitude decrease in decay rate, in reasonable accord with the observed 12% increase for 0.065 μm SD grains. For MD grains, we hypothesize that increased exposure time (slower decay) permits more efficient self‐demagnetization, reducing ARM. Low‐coercivity grains experience the largest self‐demagnetizing fields and therefore have the largest decay‐rate response. Initial‐state decay‐rate response is attributed to longer exposure times leaving domain walls more strongly pinned in deeper potential wells (the net self‐demagnetizing field is zero in the demagnetized state). Acquisition decay‐rate, annealing, and initial‐state responses of PSD grains are a blend of SD and MD responses. Because ARM is the most frequently used normalizer in relative paleointensity determination, it is important either to use a standard decay rate or else to remove the decay‐rate dependence by demagnetizing the ARM to ∼30% of its initial value (ARM0.3). A standard demagnetization level for the normalizing ARM is particularly important when comparing paleointensity records from different laboratories.

A simplified model of the formation of a deep potential well in a vacuum diode

The nonstationary problem of the formation of a virtual cathode in a diode with an accelerating electric field and a high-current electron beam entering the diode has been solved numerically. As a result, the possibility of the formation of a deep nonstationary potential well in the presence of an electric field in the diode gap has been shown, and a model for the current passage and formation of such a well in an explosive-electron-emission vacuum diode has been proposed.

Experimental studies of electrostatic confinement on the intense neutron source-electron device

Theoretical works by Barnes and Nebel [R. A. Nebel and D. C. Barnes, Fusion Technol. 38, 28 (1998); D. C. Barnes and R. A. Nebel, Phys. Plasmas 5, 2498 (1998)] have suggested that a tiny oscillating ion cloud may undergo a self-similar collapse in a harmonic oscillator potential formed by a uniform electron background. By tuning the external radio-frequency electric fields to this naturally occurring mode, it is then possible to heat the ions to obtain very high densities and temperatures simultaneously during the collapse phase of the oscillation through adiabatic compression. However, a major uncertainty in this oscillating plasma scheme is the dynamics and stability of the background electrons in the virtual cathode. Recent work based on the electron fluid equations have demonstrated that the required electron cloud is susceptible to an instability that is analogous to the Rayleigh–Taylor mode present in fluid mechanics [R. A. Nebel and J. M. Finn, Phys. Plasmas 8, 1505 (2001)]. This paper describes an inertial electrostatic confinement device at Los Alamos National Laboratory that is being used to test the electron dynamics in a virtual cathode and will subsequently be used to verify this heating and compression scheme. Results from the device operation will be presented including the formation of deep potential wells and bifurcations in the potential equilibria. A simple model is used to explain this bifurcation.

Behaviour of an optically trapped probe approaching a dielectric interface

The way in which reflection of the trapping beam from a dielectric interface influences the distance of the trapped sphere from the beam waist is studied theoretically and experimentally. The reflected wave interferes with the incident wave and they create a standing-wave component in the total axial intensity distribution. This component then modulates the trapping potential and creates several possible equilibrium positions for the trapped sphere. When the beam waist approaches the surface, the potential profile changes, which consequently causes jumps of the trapped probe from its current location to a deeper potential well. We suggested theoretically and proved experimentally that the magnitude of these unwanted jumps between the neighbouring equilibrium positions can be decreased by a suitable size of the sphere.

Black Hole Accretion Disks on the Edge

The local axisymmetric stability of hydrodynamical and magnetized, nearly-Keplerian gaseous accretion disks around non-rotating black holes is examined in the vicinity of the classical marginally-stable orbit (at radii ~ R_ms). An approximate Paczynski-Wiita pseudo-Newtonian potential is used. Hydrodynamical disks are linearly unstable inside a radius which differs slightly from the classical R_ms value because of finite pressure and radial stratification effects. Linear stresses associated with unstable hydrodynamical modes vanish exactly at the radius of marginal stability and are generally positive inside of that radius. When a magnetic field is introduced, however, the concept of radius of marginal stability becomes largely irrelevant because there are linearly unstable magneto-rotational modes everywhere. Associated linear stresses are positive and continuous across the region of hydrodynamical marginal stability, even for large-scale "hydro-like" modes subject only to weak magnetic tension. This conclusion is valid for arbitrarily thin disks (in ideal MHD) and it does not require a large-scale "radially-connecting" magnetic field. Results on hydrodynamical diskoseismic modes trapped in deep relativistic potential wells should be revised to account for the short-wavelength Alfven-like behavior of inertio-gravity waves in magnetized disks.

Collective sideband cooling in an optical ring cavity

We propose a cavity based laser cooling and trapping scheme, providing tight confinement and cooling to very low temperatures, without degradation at high particle densities. A bidirectionally pumped ring cavity builds up a resonantly enhanced optical standing wave which acts to confine polarizable particles in deep potential wells. The particle localization yields a coupling of the degenerate travelling wave modes via coherent photon redistribution. This induces a splitting of the cavity resonances with a high frequency component, that is tuned to the anti-Stokes Raman sideband of the particles oscillating in the potential wells, yielding cooling due to excess anti-Stokes scattering. Tight confinement in the optical lattice together with the prediction, that more than 50% of the trapped particles can be cooled into the motional ground state, promise high phase space densities.

Hierarchical build-up of galactic bulges and the merging rate of supermassive binary black holes

The hierarchical build-up of galactic bulges should lead to the build-up of present-day supermassive black holes by a mixture of gas accretion and merging of supermassive black holes. The tight relation between black-hole mass and stellar velocity dispersion is thereby a strong argument that the supermassive black holes in merging galactic bulges do indeed merge. Otherwise the ejection of supermassive black holes by gravitational sling-shot would lead to excessive scatter in this relation. At high redshift the coalescence of massive black-hole binaries is likely to be driven by the accretion of gas in the major mergers signposted by optically bright QSO activity. If massive black holes only form efficiently by direct collapse of gas in deep galactic potential wells with vc ≳ 100 km s−1 as postulated in the model of Kauffmann and Haehnelt (2000 Mon. Not. R. Astron. Soc. 311 576) LISA expects to see event rates from the merging of massive binary black holes of about 0.1–1 yr−1 spread over the redshift range 0 ≤ z ≤ 5. If, however, the hierarchical build-up of supermassive black holes extends to pre-galactic structures with significantly shallower potential wells, event rates may be as high as 10–100 yr−1 and will be dominated by events from redshift z ≳ 5.

Exciton–phonon coupled states in CdTe/Cd1−xZnxTe quantum dots

This article presents a theoretical analysis of the dependence of the exciton binding energy and exciton–LO-phonon coupling on the cylindrical quantum dot (QD) size. The effect of the temperature on the integrated photoluminescence line intensity is also investigated. Calculations were performed within the effective-mass approximation by using a variational method. Specific applications of these results are given for CdTe QDs embedded in a Cd1−xZnxTe matrix. The excitonic confinement is described by a finite, deep potential well. We observe, on the one hand, an enhancement of the exciton binding energy and the exciton–LO-phonon coupling energy with decreasing dot size. On the other hand, at high temperature, the LO phonon has a noticeable effect on the photoluminescence intensity. This last physical parameter also shows a great dependence on QD size and on the potential level induced by the barrier material.

Chemical localization

The possibility that, in spite of high valence electron concentrations, metal–insulator transitions can in principle occur in materials composed of atoms of only metallic elements is demonstrated based on the analysis of experimental data. For such a transition to occur, stable atomic configurations forming deep potential wells capable of trapping dozens of valence electrons should appear in the system. This means, in essence, that bulk metallic medium transforms into an assembly of identical quantum dots. Depending on the parameters, such a material either does contain delocalized electrons (metal) or does not contain such electrons (insulator). The degree of disorder is one of these parameters. Two types of substances with such properties are discussed: liquid binary alloys with both components being metallic, and thermodynamically stable quasicrystals.

Nonstatistical Dynamics in Deep Potential Wells: A Quasiclassical Trajectory Study of Methyl Loss from the Acetone Radical Cation [J. Am. Chem. Soc. 2002, 124, 8512−8513

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionNonstatistical Dynamics in Deep Potential Wells: A Quasiclassical Trajectory Study of Methyl Loss from the Acetone Radical Cation [J. Am. Chem. Soc. 2002, 124, 8512−8513]. Jeremiah A. Nummela and Barry K. CarpenterCite this: J. Am. Chem. Soc. 2002, 124, 49, 14810Publication Date (Web):November 14, 2002Publication History Published online14 November 2002Published inissue 1 December 2002https://doi.org/10.1021/ja0251165Copyright © 2002 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views299Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (20 KB) Get e-Alerts Get e-Alerts

Magnetic Properties of Short Period InGaMnAs/InGaAs Superlattices

We have observed a paramagnetic-to-ferromagnetic phase transition in short period InGaMnAs/InGaAs superlattices. The thicknesses of magnetic InGaMnAs layers in the structures studied was chosen to be 4 or 8 molecular layers (12 A or 24 A). The non-magnetic InGaAs spacer layers are 12 A thick. The composition (In content) in InGaMnAs and InGaAs was chosen in such a way that magnetic layers were: deep potential wells, high potential barriers, or shallow potential wells. For superlattices with 8 monolayer thick InGaMnAs magnetic layers and 4 monolayer thick InGaAs non-magnetic spacers the temperatures of paramagnetic-to-ferromagnetic phase transition do not depend on the band offsets between InGaMnAs and InGaAs adjusted by the In content.

Classical trajectory calculations for collision-energy/electron-energy resolved two-dimensional Penning ionization electron spectra of N2, CO, and CH3CN with metastable He*(2 3S) atoms

Collision-energy/electron-energy resolved two-dimensional Penning ionization electron spectra (2D-PIES) of N2, CO, and CH3CN with metastable He*(2 3S) atoms are measured, and classical trajectory calculations with anisotropic entrance and exit potential energy surfaces are performed for these systems. Numerical qualities of the entrance potential surfaces are decisively important to understand the collisional ionization dynamics as well as to reproduce observed 2D-PIES, whereas the exit potential surfaces are less sensitive to the collisional ionization dynamics and the electron spectra except for special cases in which a deep potential well is relevant in the entrance potential surface. Ab initio calculations of both entrance and exit potentials as well as ionization widths are found to be reliable in obtaining their anisotropy and radial dependence with good quantitative accuracy.

Nonstatistical dynamics in deep potential wells: a quasiclassical trajectory study of methyl loss from the acetone radical cation.

The loss of methyl radical from the acetone radical cation, following its formation from the enol isomer, has been found to be nonergodic. The origins of this behavior are probed computationally by a quasiclassical trajectory simulation on an AM1-SRP potential energy surface. Experimental reaction outcomes are qualitatively reproduced, and evidence is presented that coherent excitation of the CCO angle bending during isomerization is a significant factor in the nonstatistical behavior.

Channel-facilitated membrane transport: Transit probability and interaction with the channel

Transport of metabolites between cells and between subcellular compartments is facilitated by special protein channels that form aqueous pores traversing biological membranes. Accumulating evidence demonstrates that solute-specific channels display pronounced binding to the corresponding solutes. In this paper we rationalize this observation by showing that a wide and deep potential well inside the channel is able to greatly increase the transit probability of the particle through the channel. Using a one-dimensional diffusion model with radiation boundary conditions, we give exact analytical expressions for the particle translocation probabilities. We also run Brownian dynamics simulations to verify the model and the quantitative predictions of our theory.

Computer modeling of C2 cluster addition to fullerene C60

AbstractThe reaction between C2 cluster and C60 fullerene resulting in C2 insertion to C60 with formation of closed C62 cage (reaction of C2 ingestion by C60) was investigated by the semiempirical MNDO‐PM3 method. The geometries and energies of extremal points on the C62 potential energy surface were calculated. Several reaction pathways leading to the formation of three different closed C62 fullerenes were investigated. All insertion reactions proceed stepwise through intermediate adducts of different structures. The main reaction pathways were found to be addition of C2 by its one side to the 6,6‐ or 5,6‐bond of C60 with formation of primary unclosed C62 adducts of “ball‐with‐fork” structures, lying in deep potential wells. Back reaction of C2 detachment from primary adducts can compete with that of their transformation to the closed C62 cages inasmuch as calculated activation barriers of the both reactions are comparable. Model calculations at the B3LYP/6‐31G* level, using C32H12 semisphere instead of C60, confirmed the conclusion about two competitive pathways of the primary adducts transformation, C2 detachment, and C2 ingestion. The concerted insertion of C2 to C60 was realized only in the case of severe restrictions on starting geometry of the C2 + C60 system. The results of calculations explain recent experimental data on the formation of metastable adducts upon addition of C2 to C60, obtained using the time‐of‐flight mass spectrometer with laser desorption. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Comparison of Three Quantum Correction Models for the Charge Density in MOS Inversion Layers

In order to obtain high density integration for MOS devices, it is necessary to reduce the gate oxide thickness and increase the substrate doping concentration. This results in a narrow and deep potential well in which electrons are confined at the semiconductor-insulator interface and it becomes necessary to take quantum mechanical (QM) effects into consideration. In this study, we compare three well established quantum correction models, i.e., the Hansch model (Hansch W. et al. 1989. Solid State Electronics 32(10): 839–849), the modified local density approximation (MLDA) model (Paasch G. and Ubensee H. 1982. Phys. Stat. Sol. (b) 113: 165–178), and the density-gradient (D-G) model (Ancona M.G. and Tiersten H.F. 1987. Physical Review B 35(15): 7959–7965; Ancona M.G. 1997. JTCAD 97–100) in terms of accuracy for predicting the inversion layer charge distribution.