Soluble extension of the Ising model

Journal ArticleIn this note we wish to relate a somewhat trivial, but surprising, soluble extension of the multidimensional Ising model. Our extension was motivated by recent experiments on a real material, dysprosium aluminum garnet (DyAlG), which closely resembles an ideal three-dimensional Ising model,1 except for what appeared to be one unfortunate detail: The electronic (Ising) spins are connected not just to their electronic neighbors, but also to their own dysprosium nuclei by a fairly large hyperfine interaction

A New Approach To Analyzing Solar Coronal Spectra And Updated Collisional Ionization Equilibrium Calculations. II. Updated Ionization Rate Coefficients

We have re-analyzed Solar Ultraviolet Measurement of Emitted Radiation (SUMER) observations of a parcel of coronal gas using new collisional ionization equilibrium (CIE) calculations. These improved CIE fractional abundances were calculated using state-of-the-art electron-ion recombination data for K-shell, L-shell, Na-like, and Mg-like ions of all elements from H through Zn and, additionally, Al- through Ar-like ions of Fe. They also incorporate the latest recommended electron impact ionization data for all ions of H through Zn. Improved CIE calculations based on these recombination and ionization data are presented here. We have also developed a new systematic method for determining the average emission measure (EM) and electron temperature (Te ) of an isothermal plasma. With our new CIE data and a new approach for determining average EM and Te , we have re-analyzed SUMER observations of the solar corona. We have compared our results with those of previous studies and found some significant differences for the derived EM and Te . We have also calculated the enhancement of coronal elemental abundances compared to their photospheric abundances, using the SUMER observations themselves to determine the abundance enhancement factor for each of the emitting elements. Our observationally derived first ionization potential factors are in reasonable agreement with the theoretical model of Laming

Atomic vapor-based high efficiency optical detectors with photon number resolution

We propose a novel approach to the important fundamental problem of detecting weak optical fields at the few photon level. The ability to detect with high efficiency (>99%), and to distinguish the number of photons in a given time interval is a very challenging technical problem with enormous potential pay-offs in quantum communications and information processing. Our proposal diverges from standard solid-state photo-detector technology by employing an atomic vapor as the active medium, prepared in a specific quantum state using laser radiation. The absorption of a photon will be aided by a dressing laser, and the presence or absence of an excited atom will be detected using the ``cycling transition'' approach perfected for ion traps. By first incorporating an appropriate upconversion scheme, our method can be applied to a wide variety of optical wavelengths.Comment: 4 pages, 2 figure

Properties of a Polar Coronal Hole During the Solar Minimum in 2007

We report measurements of a polar coronal hole during the recent solar minimum using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Five observations are analyzed that span the polar coronal hole from the central meridian to the boundary with the quiet-Sun corona. We study the observations above the solar limb in the height range of 1.03-1.20 R ☉. The electron temperature T e and emission measure (EM) are found using a geometric mean emission measure method. The EM derived from the elements Fe, Si, S, and Al are compared in order to measure relative coronal-to-photospheric abundance enhancement factors. We also studied the ion temperature T i and the non-thermal velocity v nt using the line profiles. All these measurements are compared to polar coronal hole observations from the previous (1996-1997) solar minimum and to model predictions for relative abundances. There are many similarities in the physical properties of the polar coronal holes between the two minima at these low heights. We find that the electron density, T e, and T i are comparable in both minima. T e shows a comparable gradient with height. Both minima show a decreasing T i with increasing charge-to-mass ratio q/M. A previously observed upturn of T i for ions above q/M>0.25 was not found here. We also compared relative coronal-to-photospheric elemental abundance enhancement factors for a number of elements. These ratios were ~1 for both the low first ionization potential (FIP) elements Si and Al and the marginally high FIP element S relative to the low FIP element Fe, as is expected based on earlier observations and models for a polar coronal hole. These results are consistent with no FIP effect in a polar coronal hole

Molecular Cloud Chemistry and The Importance of Dielectronic Recombination

Dielectronic recombination (DR) of singly charged ions is a reaction pathway that is commonly neglected in chemical models of molecular clouds. In this study we include state-of-the-art DR data for He+, C+, N+, O+, Na+, and Mg+ in chemical models used to simulate dense molecular clouds, protostars, and diffuse molecular clouds. We also update the radiative recombination (RR) rate coefficients for H+, He+, C+, N+, O+, Na+, and Mg+ to the current state-of-the-art values. The new RR data have little effect on the models. However, the inclusion of DR results in significant differences in gas-grain models of dense, cold molecular clouds for the evolution of a number of surface and gas-phase species. We find differences of a factor of 2 in the abundance for 74 of the 655 species at times of 104-106 yr in this model when we include DR. Of these 74 species, 16 have at least a factor of 10 difference in abundance. We find the largest differences for species formed on the surface of dust grains. These differences are due primarily to the addition of C+ DR, which increases the neutral C abundance, thereby enhancing the accretion of C onto dust. These results may be important for the warm-up phase of molecular clouds when surface species are desorbed into the gas phase. We also note that no reliable state-of-the-art RR or DR data exist for Si+, P+, S+, Cl+, and Fe+. Modern calculations for these ions are needed to better constrain molecular cloud models

Direct Observation of the Spontaneous Emission of the Hyperfine Transition F = 4 to F = 3 in Ground State Hydrogenlike 165Ho66+ in an Electron Beam Ion Trap

We report the first direct laboratory measurement of the spontaneous emission due to the hyperfine splitting of the ground state of a highly charged hydrogenlike ion excited by electron collisions. The transition between the F = 4 and F = 3 levels of the 1s2S1/2 configuration of hydrogenlike 165Ho65+ was observed and its wavelength was determined to 5726.4±1.5Å. After taking into account relativistic, nuclear charge distribution, Bohr-Weisskopf, and QED corrections, we observe a significant deviation from commonly tabulated values of the nuclear dipole magnetic moment of this nucleu

Precision measurement of the lifetime of the 1s2s3S1 metastable level in heliumlike O6+

The lifetime of the 1s2s3S1 level of the He-like O6+ ion has been measured using the Electron Beam Ion Trap in the magnetic trapping mode. A value of 956-4+5 μs is found, which corresponds to a radiative transition rate of 1046-5+4 s-1 for the magnetic dipole transition to the 1s21S0 ground state. This value is in excellent agreement with recent theoretical predictions and distinguishes among different treatments of negative energy states and correlation in multiconfiguration Dirac-Fock calculations

A novel merged beam apparatus to study the cosmic origins of organic chemistry

Reactions of atomic carbon with molecular ions play a critical role for gas phase molecular formation in interstellar clouds. These interactions are the first links in the chain of chemical reactions leading to the synthesis of complex organic species. Much of our knowledge of this process is through spectroscopic observations and theoretical models. However, our understanding of this chemistry is constrained by uncertainties in the underlying reaction rate coefficients. Data from quantum calculations are limited to reactions involving three or fewer atoms. Meanwhile, previous experimental studies have been hampered by the difficulty in generating a sufficiently intense and well characterized neutral carbon beam. To address these issues and to study these reactions experimentally, we are building a novel laboratory device which does not suffer from such limitation

Electron capture by Ne2+ ions from atomic hydrogen

Using a merged-beam technique, the absolute, total electron-capture cross section has been measured for collisions of Ne2+ ions with hydrogen (deuterium) atoms at collision energies between 139 and 1490 eV/u. These data are compared to three other published measurements, two of which differ from one another by a factor greater than two. Early quantal rate coefficient calculations for Ne2+ ions with hydrogen at eV/u energies predict a cross section many orders of magnitude below the previously measured cross section at 40 eV/u. A possible explanation is given for the discrepancy between theory and experiment