3 results
Overview of the SPARC tokamak
- Part of
- A. J. Creely, M. J. Greenwald, S. B. Ballinger, D. Brunner, J. Canik, J. Doody, T. Fülöp, D. T. Garnier, R. Granetz, T. K. Gray, C. Holland, N. T. Howard, J. W. Hughes, J. H. Irby, V. A. Izzo, G. J. Kramer, A. Q. Kuang, B. LaBombard, Y. Lin, B. Lipschultz, N. C. Logan, J. D. Lore, E. S. Marmar, K. Montes, R. T. Mumgaard, C. Paz-Soldan, C. Rea, M. L. Reinke, P. Rodriguez-Fernandez, K. Särkimäki, F. Sciortino, S. D. Scott, A. Snicker, P. B. Snyder, B. N. Sorbom, R. Sweeney, R. A. Tinguely, E. A. Tolman, M. Umansky, O. Vallhagen, J. Varje, D. G. Whyte, J. C. Wright, S. J. Wukitch, J. Zhu, the SPARC Team
-
- Journal:
- Journal of Plasma Physics / Volume 86 / Issue 5 / October 2020
- Published online by Cambridge University Press:
- 29 September 2020, 865860502
-
- Article
-
- You have access Access
- Open access
- HTML
- Export citation
-
The SPARC tokamak is a critical next step towards commercial fusion energy. SPARC is designed as a high-field ($B_0 = 12.2$ T), compact ($R_0 = 1.85$ m, $a = 0.57$ m), superconducting, D-T tokamak with the goal of producing fusion gain $Q>2$ from a magnetically confined fusion plasma for the first time. Currently under design, SPARC will continue the high-field path of the Alcator series of tokamaks, utilizing new magnets based on rare earth barium copper oxide high-temperature superconductors to achieve high performance in a compact device. The goal of $Q>2$ is achievable with conservative physics assumptions ($H_{98,y2} = 0.7$) and, with the nominal assumption of $H_{98,y2} = 1$, SPARC is projected to attain $Q \approx 11$ and $P_{\textrm {fusion}} \approx 140$ MW. SPARC will therefore constitute a unique platform for burning plasma physics research with high density ($\langle n_{e} \rangle \approx 3 \times 10^{20}\ \textrm {m}^{-3}$), high temperature ($\langle T_e \rangle \approx 7$ keV) and high power density ($P_{\textrm {fusion}}/V_{\textrm {plasma}} \approx 7\ \textrm {MW}\,\textrm {m}^{-3}$) relevant to fusion power plants. SPARC's place in the path to commercial fusion energy, its parameters and the current status of SPARC design work are presented. This work also describes the basis for global performance projections and summarizes some of the physics analysis that is presented in greater detail in the companion articles of this collection.
ONION MAGGOT (DIPTERA: ANTHOMYIIDAE) RESISTANCE TO SOME INSECTICIDES FOLLOWING SELECTION WITH PARATHION OR CARBOFURAN
- C. R. Harris, J. H. Tolman, H. J. Svec
-
- Journal:
- The Canadian Entomologist / Volume 114 / Issue 8 / August 1982
- Published online by Cambridge University Press:
- 31 May 2012, pp. 681-685
-
- Article
- Export citation
-
An onion maggot, Hylemya antiqua (Meigen) (Diptera: Anthomyiidae) strain, having low level (≤ × 5) resistance to organophosphorus insecticides, was selected with parathion to determine if higher resistance levels to the selection agent and other insecticides used for onion maggot control would result. Parathion resistance levels increased to ×10.1 and ×23.8 after 4 and 14 generations of selection, respectively; without further selection, resistance levels declined by ca. 1/2 in 6–7 generations. Parathion resistance was ×24.4 after 20 generations of selection and resistance levels to ethion, diazinon, fonofos, and carbofuran were 2 to 3 times higher than those measured initially. The pattern of resistance development in field strains of onion maggot collected in 1975 and 1980 was similar to that observed in the laboratory selection program, but resistance levels were lower, probably because of lower selection pressure and the variety of chemicals used under practical conditions. After 14 generations of parathion selection, resistance levels were ×23.8 and ×10.1 to parathion and carbofuran, respectively. After 12 additional generations of carbofuran selection, carbofuran resistance increased to ×31.2, while the level of parathion resistance remained the same.
NMR structures of biomolecules using field oriented media and residual dipolar couplings
- J. H. Prestegard, H. M. Al-Hashimi, J. R. Tolman
-
- Journal:
- Quarterly Reviews of Biophysics / Volume 33 / Issue 4 / November 2000
- Published online by Cambridge University Press:
- 01 March 2001, pp. 371-424
-
- Article
- Export citation
-
1. Introduction 372
1.1 Residual dipolar couplings as a route to structure and dynamics 372
1.2 A brief history of oriented phase high resolution NMR 374
2. Theoretical treatment of dipolar interactions 376
2.1 Anisotropic interactions as probes of macromolecular structure and dynamics 376
2.1.1 The dipolar interaction 376
2.1.2 Averaging in the solution state 377
2.2 Ordering of a rigid body 377
2.2.1 The Saupe order tensor 378
2.2.2 Orientational probability distribution function 380
2.2.3 The generalized degree of order 380
2.3 Molecular structure and internal dynamics 381
3. Inducing molecular order in high resolution NMR 383
3.1 Tensorial interactions between the magnetic field and anisotropic magnetic susceptibilities 383
3.2 Dilute liquid crystal media: a tunable source of order 384
3.2.1 Bicelles : from membrane mimics to aligning media 385
3.2.2 Filamentous phage 387
3.2.3 Transfer of alignment from ordered media to macromolecules 388
3.3 Magnetic field alignment 389
3.3.1 Paramagnetic assisted alignment 389
3.3.2 Advantages of using magnetic alignment 389
4. The measurement of residual dipolar couplings 391
4.1 Introduction 391
4.2 Frequency based methods 392
4.2.1 Coupling enhanced pulse schemes 392
4.2.2 In phase anti-phase methods (IPAP): 1DNH couplings in proteins 393
4.2.3 Exclusive correlated spectroscopy (E-COSY): 1DNH, 1DNC′ and 2DHNC′ 395
4.2.4 Extraction of splitting values from the frequency domain 396
4.3 Intensity based experiments 397
4.3.1 J-Modulated experiments: the measurement of 1DCαHα in proteins 397
4.3.2 Phase modulated methods 399
4.3.3 Constant time COSY – the measurement of DHH couplings 399
4.3.4 Systematic errors in intensity based experiments 400
5. Interpretation of residual dipolar coupling data 401
5.1 Structure determination protocols utilizing orientational constraints 401
5.1.1 The simulated annealing approach 401
5.1.2 Order matrix analysis of dipolar couplings 402
5.1.3 A discussion of the two approaches 402
5.2 Reducing orientational degeneracy 403
5.2.1 Multiple alignment media in the simulated annealing approach 404
5.2.2 Multiple alignment media in the order matrix approach 405
5.3 Simplifying effects arising due to molecular symmetry 406
5.4 Database approaches for determining protein structure 407
6. Applications to the characterization of macromolecular systems 408
6.1 Protein structure refinement 408
6.2 Protein domain orientation 409
6.3 Oligosaccharides 413
6.4 Biomolecular complexes 415
6.5 Exchanging systems 416
7. Acknowledgements 418
8. References 419
Within its relatively short history, nuclear magnetic resonance (NMR) spectroscopy has managed to play an important role in the characterization of biomolecular structure. However, the methods on which most of this characterization has been based, Nuclear Overhauser Effect (NOE) measurements for short-range distance constraints and scalar couplings measurements for torsional constraints, have limitations (Wüthrich, 1986). For extended structures, such as DNA helices, for example, propagation of errors in the short distance constraints derived from NOEs leaves the relative orientation of remote parts of the structures poorly defined. Also, the low density of observable protons in contact regions of molecules held together by factors other than hydrophobic packing, leads to poorly defined structures. This is especially true in carbohydrate containing complexes where hydrogen bonds often mediate contacts, and in multi-domain proteins where the area involved in domain–domain contact can also be small. Moreover, most NMR based structural applications are concerned with the characterization of a single, rigid conformer for the final structure. This can leave out important mechanistic information that depends on dynamic aspects and, when motion is present, this can lead to incorrect structural representations. This review focuses on one approach to alleviating some of the existing limitations in NMR based structure determination: the use of constraints derived from the measurement of residual dipolar couplings (D).