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Indirect study of (11)B(p,alpha(0))(8)Be and (10)B(p,alpha)(7)Be reactions at astrophysical energies by means of the Trojan Horse Method: recent results

LAMIA, L.; PUGLIA, S. M. R.; SPITALERI, C.; ROMANO, S.; SANTO, M. Gimenez Del; Carlin Filho, Nelson; Munhoz, Marcelo Gameiro; CHERUBINI, S.; KISS, G. G.; KROHA, V.; KUBONO, S.; COGNATA, M. La; LI, Cheng-Bo; PIZZONE, R. G.; WEN, Qun-Gang; SERGI, M. L.; Sza
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.68%
Nuclear (p,alpha) reactions destroying the so-called ""light-elements"" lithium, beryllium and boron have been largely studied in the past mainly because their role in understanding some astrophysical phenomena, i.e. mixing-phenomena occurring in young F-G stars [1]. Such mechanisms transport the surface material down to the region close to the nuclear destruction zone, where typical temperatures of the order of similar to 10(6) K are reached. The corresponding Gamow energy E(0)=1.22 (Z(x)(2)Z(X)(2)T(6)(2))(1/3) [2] is about similar to 10 keV if one considers the ""boron-case"" and replaces in the previous formula Z(x) = 1, Z(X) = 5 and T(6) = 5. Direct measurements of the two (11)B(p,alpha(0))(8)Be and (10)B(p,alpha)(7)Be reactions in correspondence of this energy region are difficult to perform mainly because the combined effects of Coulomb barrier penetrability and electron screening [3]. The indirect method of the Trojan Horse (THM) [4-6] allows one to extract the two-body reaction cross section of interest for astrophysics without the extrapolation-procedures. Due to the THM formalism, the extracted indirect data have to be normalized to the available direct ones at higher energies thus implying that the method is a complementary tool in solving some still open questions for both nuclear and astrophysical issues [7-12].

Modeling of laser-generated radiative blast waves, with applications to late-term supernova remnants

Keilty, Katherine Anne
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
35.74%
The goal of laser astrophysics is to provide a means by which aspects of specific astrophysical phenomena can be reproduced in the laboratory. Although the hydrodynamic instabilities of early supernova remnants have already been studied using this method, the role of significant radiative losses in shock propagation (for example, in late-term remnants) has only been imperfectly modeled. This thesis introduces an improved self-similar analytic approach to radiative blast-wave evolution where the total amount of energy loss remains constant in proportion to the energy flux entering the shock front. The approximation is solved for the cases in which both energy loss from the shock front and heating of the shock (due to the presence of ionization precursors) are significant. Because this solution is independent of the exact method of cooling, it is appropriate for both the laboratory and astrophysical regimes. In addition, this thesis applies the analytic approximation to laboratory-produced radiative blast waves as well as to numerical models of these experimental blast waves. These results will allow for better design of laser-based experiments with further applications to astrophysical phenomena, as well as for an increase in the understanding of the challenges involved in scaling radiative phenomena between laboratory experiments and astrophysical theory.

Conservative special relativistic radiative transfer for multidimensional astrophysical simulations: motivation and elaboration

Cardall, Christian Y.; Lentz, Eric J.; Mezzacappa, Anthony
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/10/2005
Relevância na Pesquisa
45.57%
Many astrophysical phenomena exhibit relativistic radiative flows. While velocities in excess of $v \sim 0.1c$ can occur in these systems, it has been common practice to approximate radiative transfer to $\cO(v/c)$. In the case of neutrino transport in core-collapse supernovae, this approximation gives rise to an inconsistency between the lepton number transfer and lab frame energy transfer, which have different $\cO(v/c)$ limits. A solution used in spherically symmetric $\cO(v/c)$ simulations has been to retain, for energy accounting purposes, the $\cO(v^2/c^2)$ terms in the lab frame energy transfer equation that arise from the $\cO(v/c)$ neutrino number transport equation. Avoiding the proliferation of such ``extra'' $\cO(v^2/c^2)$ terms in the absence of spherical symmetry motivates a special relativistic formalism, which we exhibit in coordinates sufficiently general to encompass Cartesian, spherical, and cylindrical coordinate systems.; Comment: 9 pages

Ongoing Space Physics - Astrophysics Connections

Eichler, David
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/03/2005
Relevância na Pesquisa
35.56%
I review several ongoing connections between space physics and astrophysics: a) Measurements of energetic particle spectra have confirmed theoretical prediction of the highest energy to which shocks can accelerate particles, and this has direct bearing on the origin of the highest energy cosmic rays. b) Mass ejection in solar flares may help us understand photon ejection in the giant flares of magnetar outbursts. c) Measurements of electron heat fluxes in the solar wind can help us understand whether heat flux in tenuous astrophysical plasma is in accordance with the classical Spitzer-Harm formula or whether it is reduced well below this value by plasma instabilities.; Comment: To appear in Proceedings of "Critical Phenomena in the Solar System", Ein-Boqeq, March, 2004

Large collection of astrophysical S-factors and its compact representation

Afanasjev, A. V.; Beard, M.; Chugunov, A. I.; Wiescher, M.; Yakovlev, D. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/04/2012
Relevância na Pesquisa
35.57%
Numerous nuclear reactions in the crust of accreting neutron stars are strongly affected by dense plasma environment. Simulations of superbursts, deep crustal heating and other nuclear burning phenomena in neutron stars require astrophysical S-factors for these reactions (as a function of center-of-mass energy E of colliding nuclei). A large database of S-factors is created for about 5000 non-resonant fusion reactions involving stable and unstable isotopes of Be, B, C, N, O, F, Ne, Na, Mg, and Si. It extends the previous database of about 1000 reactions involving isotopes of C, O, Ne, and Mg. The calculations are performed using the Sao Paulo potential and the barrier penetration formalism. All calculated S-data are parameterized by an analytic model for S(E) proposed before [Phys. Rev. C 82, 044609 (2010)] and further elaborated here. For a given reaction, the present S(E)-model contains three parameters. These parameters are easily interpolated along reactions involving isotopes of the same elements with only seven input parameters, giving an ultracompact, accurate, simple, and uniform database. The S(E) approximation can also be used to estimate theoretical uncertainties of S(E) and nuclear reaction rates in dense matter, as illustrated for the case of the 34Ne+34Ne reaction in the inner crust of an accreting neutron star.; Comment: 13 pages...

Dark Energy Stars

Chapline, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.47%
Event horizons and closed time-like curves cannot exist in the real world for the simple reason that they are inconsistent with quantum mechanics. Following ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago, and the speaker it is now possible to describe in some detail what happens physically when one approaches and crosses a region of space-time where classical general relativity predicts there should be an infinite red shift surface. This quantum critical physics provides a new perspective on a variety of enigmatic astrophysical phenomena, including supernovae explosions, gamma ray bursts, positron emission, and dark matter.; Comment: 4 pages, 2 figures, corrected typos

Astrophysical Observations: Lensing and Eclipsing Einstein's Theories

Bennett, Charles L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/03/2005
Relevância na Pesquisa
45.58%
Albert Einstein postulated the equivalence of energy and mass, developed the theory of special relativity, explained the photoelectric effect, and described Brownian motion in five papers, all published in 1905, 100 years ago. With these papers, Einstein provided the framework for understanding modern astrophysical phenomena. Conversely, astrophysical observations provide one of the most effective means for testing Einstein's theories. Here, I review astrophysical advances precipitated by Einstein's insights, including gravitational redshifts, gravitational lensing, gravitational waves, the Lense-Thirring effect, and modern cosmology. A complete understanding of cosmology, from the earliest moments to the ultimate fate of the universe, will require developments in physics beyond Einstein, to a unified theory of gravity and quantum physics.; Comment: 6 pages, 4 figures (resol. Reduced to 85 dpi)

Radiation hydrodynamics integrated in the code PLUTO

Kolb, Stefan M.; Stute, Matthias; Kley, Wilhelm; Mignone, Andrea
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/09/2013
Relevância na Pesquisa
35.54%
The transport of energy through radiation is very important in many astrophysical phenomena. In dynamical problems the time-dependent equations of radiation hydrodynamics have to be solved. We present a newly developed radiation-hydrodynamics module specifically designed for the versatile MHD code PLUTO. The solver is based on the flux-limited diffusion approximation in the two-temperature approach. All equations are solved in the co-moving frame in the frequency independent (grey) approximation. The hydrodynamics is solved by the different Godunov schemes implemented in PLUTO, and for the radiation transport we use a fully implicit scheme. The resulting system of linear equations is solved either using the successive over-relaxation (SOR) method (for testing purposes), or matrix solvers that are available in the PETSc library. We state in detail the methodology and describe several test cases in order to verify the correctness of our implementation. The solver works in standard coordinate systems, such as Cartesian, cylindrical and spherical, and also for non-equidistant grids. We have presented a new radiation-hydrodynamics solver coupled to the MHD-code \PLUTO that is a modern, versatile and efficient new module for treating complex radiation hydrodynamical problems in astrophysics. As test cases...

Early attempts at atmospheric simulations for the Cherenkov Telescope Array

Rulten, Cameron B.; consortium, Sam J. Nolan for the CTA
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.51%
The Cherenkov Telescope Array (CTA) will be the world's first observatory for detecting gamma-rays from astrophysical phenomena and is now in its prototyping phase with construction expected to begin in 2015/16. In this work we present the results from early attempts at detailed simulation studies performed to assess the need for atmospheric monitoring. This will include discussion of some lidar analysis methods with a view to determining a range resolved atmospheric transmission profile. We find that under increased aerosol density levels, simulated gamma-ray astronomy data is systematically shifted leading to softer spectra. With lidar data we show that it is possible to fit atmospheric transmission models needed for generating lookup tables, which are used to infer the energy of a gamma-ray event, thus making it possible to correct affected data that would otherwise be considered unusable.; Comment: 5 pages, 6 figures, updated author metadata

Effects of Environment and Energy Injection on Gamma-Ray Burst Afterglows

Dai, Z. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/08/2000
Relevância na Pesquisa
35.57%
There is growing evidence that some long gamma-ray bursts (GRBs) arise from the core collapse of massive stars, and thus it is inevitable that the environments of these GRBs are preburst stellar winds or dense media. We studied, for the first time, the wind model for afterglows based on the Blandford-McKee self-similar solution of a relativistic shock, and suggested that GRB 970616 is an interactor with a stellar wind. We also proposed a dense medium model for some afterglows, e.g., the steepening in the light curve of the R-band afterglow of GRB 990123 may be caused by the adiabatic shock which has evolved from an ultrarelativistic phase to a nonrelativistic phase in a dense medium. We further discussed the dense medium model in more details, and investigated the effects of synchrotron self absorption and energy injection. A shock in a dense medium becomes nonrelativistic rapidly after a short relativistic phase. The afterglow from the shock at the nonrelativistic stage decays more rapidly than at the relativistic stage. Since some models for GRB energy sources predicted that a strongly magnetic millisecond pulsar may be born during GRB formation, we discussed the effect of such a pulsar on the evolution of the nonrelativistic shock through magnetic dipole radiation. We found that in the pulsar energy injection case...

Magnetic Extraction of Spin Energy from a Black Hole

Krolik, Julian H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/08/2000
Relevância na Pesquisa
35.56%
Numerous variations have been proposed on the original suggestion by Blandford and Znajek that magnetic fields could be used to extract rotational energy from black holes. A new categorization of these variations is proposed so that they may be considered in a systematic way. "Black hole spindown" is defined more precisely, distinguishing decrease in the spin parameter a/M from decreases in angular momentum a and rotational kinetic energy, M - M_i. Several key physical questions are raised: Can the "stretched horizon" of a black hole communicate with the outside world? Do accretion disks bring any net magnetic flux to the black holes at their centers? Is the magnetic field adjacent to a black hole force-free everywhere?; Comment: to appear in "Explosive Phenomena in Astrophysical Compact Objects, Proceedings of the 1st KIAS Astrophysics Workshop"

Nuclear Astrophysics with Radioactive Beams

Bertulani, C. A.; Gade, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.55%
The quest to comprehend how nuclear processes influence astrophysical phenomena is driving experimental and theoretical research programs worldwide. One of the main goals in nuclear astrophysics is to understand how energy is generated in stars, how elements are synthesized in stellar events and what the nature of neutron stars is. New experimental capabilities, the availability of radioactive beams and increased computational power paired with new astronomical observations have advanced the present knowledge. This review summarizes the progress in the field of nuclear astrophysics with a focus on the role of indirect methods and reactions involving beams of rare isotopes.; Comment: 121 pages, 27 figures, 510 references, to appear in Physics Reports. Minor typos and references fixed

Three-Dimensional Magnetic Reconnection

Parnell, Clare E.; Haynes, Andrew L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/03/2009
Relevância na Pesquisa
35.59%
The importance of magnetic reconnection as an energy release mechanism in many solar, stellar, magnetospheric and astrophysical phenomena has long been recognised. Reconnection is the only mechanism by which magnetic fields can globally restructure, enabling them to access a lower energy state. Over the past decade, there have been some major advances in our understanding of three-dimensional reconnection. In particular, the key characteristics of 3D magnetohydrodynamic (MHD) reconnection have been determined. For instance, 3D reconnection (i) occurs with or without nulls, (ii) occurs continuously and continually throughout a diffusion region and (iii) is driven by counter rotating flows. Furthermore, analysis of resistive 3D MHD magnetic experiments have revealed some intriguing effects relating to where and how reconnection occurs. To illustrate these new features, a series of constant-resistivity experiments, involving the interaction of two opposite-polarity magnetic sources in an overlying field, are considered. Such a simple interaction represents a typical building block of the Sun's magnetic atmosphere. By following the evolution of the magnetic topology, we are able to explain where, how and at what rate the reconnection occurs. Remarkably there can be up to five energy release sites at anyone time (compared to one in the potential case) and the duration of the interaction increases (more than doubles) as the resistivity decreases (by a factor of 16). The decreased resistivity also leads to a higher peak ohmic dissipation and more energy being released in total...

Periodic Box FHNC calculations of neutron star crustal matter. (I)

Bassan, Nicola; Fantoni, Stefano; Schmidt, Kevin E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/06/2011
Relevância na Pesquisa
35.51%
Neutron star crustal matter, whose properties are relevant in many models aimed at explaining observed astrophysical phenomena, has so far always been studied using a mean field approach. In order to check the results obtained in this way, a sensible next step is to make use of a realistic nuclear potential. The present paper extends the periodic-box Fermi HyperNetted Chain method to include longitudinal-isospin dependence of the correlations, making feasible a study of asymmetric crustal matter. Results are presented for the symmetry energy, the low-density neutron star equation of state and the single particle neutron and proton energies.; Comment: 27 pages, submitted to PRC

Rydberg atoms in astrophysics

Gnedin, Yu. N.; Mihajlov, A. A.; Ignjatovic, Lj. M.; Sakan, N. M.; Sreckovic, V. A.; Zakharov, M. Yu.; Bezuglov, N. N.; Klycharev, A. N.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/08/2012
Relevância na Pesquisa
45.53%
Elementary processes in astrophysical phenomena traditionally attract researchers attention. At first this can be attributed to a group of hemi-ionization processes in Rydberg atom collisions with ground state parent atoms. This processes might be studied as a prototype of the elementary process of the radiation energy transformation into electrical one. The studies of nonlinear mechanics have shown that so called regime of dynamic chaos should be considered as typical, rather than exceptional situation in Rydberg atoms collision. From comparison of theory with experimental results it follows that a such kind of stochastic dynamic processes, occurred during the single collision, may be observed.

A Macroscopic Description of a Generalized Self-Organized Criticality System: Astrophysical Applications

Aschwanden, Markus J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.6%
We suggest a generalized definition of self-organized criticality (SOC) systems: SOC is a critical state of a nonlinear energy dissipation system that is slowly and continuously driven towards a critical value of a system-wide instability threshold, producing scale-free, fractal-diffusive, and intermittent avalanches with powerlaw-like size distributions. We develop here a macroscopic description of SOC systems that provides an equivalent description of the complex microscopic fine structure, in terms of fractal-diffusive transport (FD-SOC). Quantitative values for the size distributions of SOC parameters (length scales $L$, time scales $T$, waiting times $\Delta t$, fluxes $F$, and energies $E$) are derived from first principles, using the scale-free probability conjecture, $N(L) dL \propto L^{-d}$, for Euclidean space dimension $d$. We apply this model to astrophysical SOC systems, such as lunar craters, the asteroid belt, Saturn ring particles, magnetospheric substorms, radiation belt electrons, solar flares, stellar flares, pulsar glitches, soft gamma-ray repeaters, black-hole objects, blazars, and cosmic rays. The FD-SOC model predicts correctly the size distributions of 8 out of these 12 astrophysical phenomena, and indicates non-standard scaling laws and measurement biases for the others.

Magnetic Energy and Helicity Budgets in the Active-Region Solar Corona. I. Linear Force-Free Approximation

Georgoulis, M. K.; LaBonte, Barry J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/06/2007
Relevância na Pesquisa
35.54%
We self-consistently derive the magnetic energy and relative magnetic helicity budgets of a three-dimensional linear force-free magnetic structure rooted in a lower boundary plane. For the potential magnetic energy we derive a general expression that gives results practically equivalent to those of the magnetic Virial theorem. All magnetic energy and helicity budgets are formulated in terms of surface integrals applied to the lower boundary, thus avoiding computationally intensive three-dimensional magnetic field extrapolations. We analytically and numerically connect our derivations with classical expressions for the magnetic energy and helicity, thus presenting a so-far lacking unified treatment of the energy/helicity budgets in the constant-alpha approximation. Applying our derivations to photospheric vector magnetograms of an eruptive and a noneruptive solar active regions, we find that the most profound quantitative difference between these regions lies in the estimated free magnetic energy and relative magnetic helicity budgets. If this result is verified with a large number of active regions, it will advance our understanding of solar eruptive phenomena. We also find that the constant-alpha approximation gives rise to large uncertainties in the calculation of the free magnetic energy and the relative magnetic helicity. Therefore...

Evolution of Solar Magnetic Field and Associated Multi-wavelength Phenomena: Flare events on 20 November 2003

Kumar, Pankaj; Manoharan, P. K.; Uddin, Wahab
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/12/2009
Relevância na Pesquisa
35.56%
We analyze H-alpha images, soft X-ray profiles, magnetograms, extreme ultra-violet images and radio observations of two homologous flare events (M1.4/1N and M9.6/2B) on 20 November 2003 in the active region NOAA 10501 and study properties of reconnection between twisted filament systems, energy release and associated launch of coronal mass ejections (CMEs). During both events twisted filaments observed in H-alpha approached each other and initiated the flare processes. However, the second event showed the formation of cusp as the filaments interacted. The rotation of sunspots of opposite polarities, inferred from magnetograms likely powered the twisted filaments and injection of helicity. Along the current sheet between these two opposite polarity sunspots, the shear was maximum, which could have caused the twist in the filament. At the time of interaction between filaments, the reconnection took place and flare emission in thermal and non-thermal energy ranges attained the maximum. The radio signatures revealed the opening of field lines resulting from reconnection. The H-alpha images and radio data provide the inflow speed leading to reconnection and the scale size of particle acceleration region. The first event produced a narrow and slow CME...

A localised subgrid scale model for fluid dynamical simulations in astrophysics I: Theory and numerical tests

Schmidt, W.; Niemeyer, J. C.; Hillebrandt, W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/01/2006
Relevância na Pesquisa
45.54%
We present a one-equation subgrid scale model that evolves the turbulence energy corresponding to unresolved velocity fluctuations in large eddy simulations. The model is derived in the context of the Germano consistent decomposition of the hydrodynamical equations. The eddy-viscosity closure for the rate of energy transfer from resolved toward subgrid scales is localised by means of a dynamical procedure for the computation of the closure parameter. Therefore, the subgrid scale model applies to arbitrary flow geometry and evolution. For the treatment of microscopic viscous dissipation a semi-statistical approach is used, and the gradient-diffusion hypothesis is adopted for turbulent transport. A priori tests of the localised eddy-viscosity closure and the gradient-diffusion closure are made by analysing data from direct numerical simulations. As an a posteriori testing case, the large eddy simulation of thermonuclear combustion in forced isotropic turbulence is discussed. We intend the formulation of the subgrid scale model in this paper as a basis for more advanced applications in numerical simulations of complex astrophysical phenomena involving turbulence.; Comment: 18 pages, 10 figures, accepted for publication in Astron. Astrophys.; 3D visualisations not included; complete PDF version can be downloaded from http://www.astro.uni-wuerzburg.de/%7Eschmidt/Paper/SGSModel_I_AA.pdf

Investigation of thermonuclear $^{18}$Ne($\alpha$,$p$)$^{21}$Na rate via resonant elastic scattering of $^{21}$Na+$p$

Zhang, L. Y.; He, J. J.; Parikh, A.; Xu, S. W.; Yamaguchi, H.; Kahl, D.; Kubono, S.; Mohr, P.; Hu, J.; Ma, P.; Chen, S. Z.; Wakabayashi, Y.; Wang, H. W.; Tian, W. D.; Chen, R. F.; Guo, B.; Hashimoto, T.; Togano, Y.; Hayakawa, S.; Teranishi, T.; Iwasa, N.;
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/03/2014
Relevância na Pesquisa
35.57%
The $^{18}$Ne($\alpha$,$p$)$^{21}$Na reaction is thought to be one of the key breakout reactions from the hot CNO cycles to the rp-process in type I x-ray bursts. In this work, the resonant properties of the compound nucleus $^{22}$Mg have been investigated by measuring the resonant elastic scattering of $^{21}$Na+$p$. An 89 MeV $^{21}$Na radioactive beam delivered from the CNS Radioactive Ion Beam Separator bombarded an 8.8 mg/cm$^2$ thick polyethylene (CH$_{2}$)$_{n}$ target. The $^{21}$Na beam intensity was about 2$\times$10$^{5}$ pps, with a purity of about 70% on target. The recoiled protons were measured at the center-of-mass scattering angles of $\theta_{c.m.}$$\approx$175.2${^\circ}$, 152.2${^\circ}$, and 150.5${^\circ}$ by three sets of $\Delta E$-$E$ telescopes, respectively. The excitation function was obtained with the thick-target method over energies $E_x$($^{22}$Mg)=5.5--9.2 MeV. In total, 23 states above the proton-threshold in $^{22}$Mg were observed, and their resonant parameters were determined via an $R$-matrix analysis of the excitation functions. We have made several new $J^{\pi}$ assignments and confirmed some tentative assignments made in previous work. The thermonuclear $^{18}$Ne($\alpha$,$p$)$^{21}$Na rate has been recalculated based on our recommended spin-parity assignments. The astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the $^{18}$Ne($\alpha$...