| 1. |
- Wood-Vasey, W. M., et al.
(author)
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Observational constraints on the nature of dark energy : First cosmological results from the ESSENCE supernova survey
- 2007
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 666:2, s. 694-715
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Research review (peer-reviewed)abstract
- We present constraints on the dark energy equation-of-state parameter, w = P/(rho c(2)), using 60 SNe Ia fromthe ESSENCE supernova survey. We derive a set of constraints on the nature of the dark energy assuming a flat universe. By including constraints on (Omega(M), w) from baryon acoustic oscillations, we obtain a value for a static equation-of-state parameter w = -1:05(-0.12)(+0: 13) (stat 1 sigma) +/- 0: 13 (sys) and Omega(M) = 0:274(-0.020)(+0:033) (stat 1 sigma) with a bestfit chi(2)/dof of 0.96. These results are consistent with those reported by the Supernova Legacy Survey from the first year of a similar program measuring supernova distances and redshifts. We evaluate sources of systematic error that afflict supernova observations and present Monte Carlo simulations that explore these effects. Currently, the largest systematic with the potential to affect our measurements is the treatment of extinction due to dust in the supernova host galaxies. Combining our set of ESSENCE SNe Ia with the first-results Supernova Legacy Survey SNe Ia, we obtain a joint constraint of w = -1:07(-0: 09)(+0:09) (stat 1 sigma) +/- 0: 13 ( sys), Omega(M) 0:267(-0:028)(+0:028) (stat 1 sigma) with a best-fit chi(2)/dof of 0.91. The current global SN Ia data alone rule out empty (Omega(M) = 0), matter-only Omega(M) = 0: 3, and Omega(M) = 1 universes at > 4.5 sigma. The current SN Ia data are fully consistent with a cosmological constant.
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| 2. |
- Miknaitis, G., et al.
(author)
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The ESSENCE supernova survey : Survey optimization, observations, and supernova photometry
- 2007
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 666:2, s. 674-693
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Research review (peer-reviewed)abstract
- We describe the implementation and optimization of the ESSENCE supernova survey, which we have undertaken to measure the dark energy equation-of-state parameter, w = P/(rho c(2)). We present a method for optimizing the survey exposure times and cadence to maximize our sensitivity to w for a given fixed amount of telescope time. For our survey on the CTIO 4 m telescope, measuring the luminosity distances and redshifts for supernovae at modest redshifts (z approximate to 0: 5 +/- 0: 2) is optimal for determining w. We describe the data analysis pipeline based on using reliable and robust image subtraction to find supernovae automatically and in nearly real time. Since making cosmological inferences with supernovae relies crucially on accurate measurement of their apparent brightnesses, we describe our efforts to establish a thorough calibration of the CTIO 4 m telescope's natural photometric system. In its first four years, ESSENCE has discovered and spectroscopically confirmed 102 Type Ia supernovae, at redshifts from 0.10 to 0.78, identified through an impartial, effective methodology for spectroscopic classification and redshift determination. We present the resulting light curves for all of the Type Ia supernovae found by ESSENCE and used in our measurement of w, presented in a companion paper by Wood-Vasey and coworkers.
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| 3. |
- Narayan, G., et al.
(author)
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LIGHT CURVES OF 213 TYPE Ia SUPERNOVAE FROM THE ESSENCE SURVEY
- 2016
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In: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 224:1
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Journal article (peer-reviewed)abstract
- The ESSENCE survey discovered 213 Type Ia supernovae at redshifts 0.1 < z < 0.81 between 2002 and 2008. We present their R- and I-band photometry, measured from images obtained using the MOSAIC II camera at the CTIO Blanco, along with rapid-response spectroscopy for each object. We use our spectroscopic follow-up observations to determine an accurate, quantitative classification, and precise redshift. Through an extensive calibration program we have improved the precision of the CTIO Blanco natural photometric system. We use several empirical metrics to measure our internal photometric consistency and our absolute calibration of the survey. We assess the effect of various potential sources of systematic bias on our measured fluxes, and estimate the dominant term in the systematic error budget from the photometric calibration on our absolute fluxes is similar to 1%.
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| 4. |
- Burgos-Parra, E., et al.
(author)
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Investigation of magnetic droplet solitons using x-ray holography with extended references
- 2018
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Journal article (peer-reviewed)abstract
- A dissipative magnetic soliton, or magnetic droplet, is a structure that has been predicted to exist within a thin magnetic layer when non-linearity is balanced by dispersion, and a driving force counteracts the inherent damping of the spin precession. Such a soliton can be formed beneath a nano-contact (NC) that delivers a large spin-polarized current density into a magnetic layer with perpendicular magnetic anisotropy. Although the existence of droplets has been confirmed from electrical measurements and by micromagnetic simulations, only a few attempts have been made to directly observe the magnetic landscape that sustains these structures, and then only for a restricted set of experimental parameter values. In this work we use and x-ray holography technique HERALDO, to image the magnetic structure of the [ Co/ Ni] x4 multilayer within a NC orthogonal pseudo spin-valve, for different range of magnetic fields and injected electric currents. The magnetic configuration imaged at -33 mA and 0.3 T for devices with 90 nm NC diameter reveals a structure that is within the range of current where the droplet soliton exist based on our electrical measurements and have it is consistent with the expected size of the droplet (similar to 100 nm diameter) and its spatial position within the sample. We also report the magnetisation configurations observed at lower DC currents in the presence of fields (0-50 mT), where it is expected to observe regimes of the unstable droplet formation.
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| 5. |
- Bernhard, M, et al.
(author)
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Institutional Subsystems and the Survival of Democracy: Do Political and Civil Society Matter?
- 2015
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Other publication (other academic/artistic)abstract
- How do two central institutional subsystems of democracy – party systems and civil society –affect the persistence of democratic regimes?Despite the ability of each of these institutions to provide sources of countervailing power that make politicians accountable and thus responsive, distributionist accounts of democratic breakdown provide few insights on how such institutions may encourage parties to reach accommodation. We argue that these institutions provide credible threats against anti-system activities that would otherwise threaten the democratic compromise. We test our argument with newly available data from the Varieties of Democracy (V-Dem) project by analyzing all episodes of democratic breakdown from 1900 -2001. Using a split population event history estimator, we find evidence that these institutions not only forestall the timing of breakdowns among transitional democracies but also that a strong party system is critical to setting democratic regimes on the path of consolidation.
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| 6. |
- Bernhard, M., et al.
(author)
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Parties, Civil Society, and the Deterrence of Democratic Defection
- 2020
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In: Studies in Comparative International Development. - : Springer Science and Business Media LLC. - 0039-3606 .- 1936-6167. ; 55, s. 1-26
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Journal article (peer-reviewed)abstract
- The third wave of democratization has given way to a reverse wave of autocratization. A critical question is what can be done to prevent democratic breakdowns and make democracy endure. A large body of historical-narrative and small-N comparative scholarship has suggested that an active mobilized civil society and institutionalized political parties can be mobilized to protect democracy from authoritarian takeovers. We provide the first rigorous set of empirical analyses to test this argument using data from the Varieties of Democracy (V-Dem) project for the period from 1900 to 2010. We find that both exert a robust, independent, and substantial effect on the survival of democracies. These findings have important policy implications for the international community.
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| 7. |
- Coppedge, M, et al.
(author)
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Conceptualizing and Measuring Democracy: A New Approach
- 2011
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In: Perspectives on Politics. - 1537-5927 .- 1541-0986. ; 9:2, s. 247-267
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Journal article (peer-reviewed)abstract
- In the wake of the Cold War, democracy has gained the status of a mantra. Yet there is no consensus about how to conceptualize and measure regimes such that meaningful comparisons can be made through time and across countries. In this prescriptive article, we argue for a new approach to conceptualization and measurement. We first review some of the weaknesses among traditional approaches. We then lay out our approach, which may be characterized as historical, multidimensional, disaggregated, and transparent. We end by reviewing some of the payoffs such an approach might bring to the study of democracy.
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| 8. |
- Parra, Erick O. Burgos, et al.
(author)
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Holographic Magnetic Imaging of Single-Layer Nanocontact Spin-Transfer Oscillators
- 2016
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In: IEEE transactions on magnetics. - : IEEE. - 0018-9464 .- 1941-0069. ; 52:7
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Journal article (peer-reviewed)abstract
- Time-averaged images of the magnetization within single-layer spin-transfer oscillators have been obtained using the holography with extended reference by autocorrelation linear differential operator technique. Transport measurements on a Pd(5)-Cu(20)-Ni81Fe19(7)-Cu(2)-Pd(2) (in nanometers) stack with a 100 nm diameter nanocontact reveal the presence of vortex dynamics. Magnetic images of the device for injected current values of 24 and -24 mA suggest that a vortex has been ejected from the nanocontact and become pinned at the edge of the region that is visible through the Au mask.
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