470 research outputs found
Nonlinear ptychographic coherent diffractive imaging
Ptychographic Coherent diffractive imaging (PCDI) is a significant advance in imaging allowing the measurement of the full electric field at a sample without use of any imaging optics. So far it has been confined solely to imaging of linear optical responses. In this paper we show that because of the coherence-preserving nature of nonlinear optical interactions, PCDI can be generalised to nonlinear optical imaging. We demonstrate second harmonic generation PCDI, directly revealing phase information about the nonlinear coefficients, and showing the general applicability of PCDI to nonlinear interactions
The Effects of IVC Modulation on Modern Diesel Engines Equipped with Variable Valve Actuation at High Load and Speed
Modern diesel compression engines are known for their increased durability, fuel economy and torque when compared with their spark ignition gasoline counterparts. These are some of the reasons why diesel engines are preferred in heavy duty applications such as trains and semi-trucks. During the Heavy Duty Federal Test Procedure transient drive cycle, or HDFTP, nearly 85% of the total fuel burned is at speeds greater than 2000 revolutions per minute (RPM) for the studied engine. Therefore, it is desirable to increase the fuel economy at these loads and speeds. It is hypothesized that the use of late intake valve close timing (LIVC) modulation could give an increase in volumetric efficiency from flow momentum. With an increase in volumetric efficiency, the open cycle efficiency (OCE) would increase. This would allow for improvements in the brake thermal efficiency (BTE). With the use of the engine simulator software GT-Power, the effects of IVC variation was explored to serve as a preliminary investigation for a variable valve actuation (VVA) engine in the future. The results from this investigation yielded an increase in volumetric efficiency through late intake valve closure (LIVC). While these findings have not been verified through experimental procedures, there could be a decrease in BSFC because the engine could breathe more efficiently, thereby reducing pumping losses
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Ambient solar wind's effect on ICME transit times
Most empirical and numerical models of Interplanetary Coronal Mass Ejection (ICME) propagation use the initial CME velocity as their primary, if not only, observational input. These models generally predict a wide spread of 1 AU transit times for ICMEs with the same initial velocity. We use a 3D coupled MHD model of the corona and heliosphere to determine the ambient solar wind's effect on the propagation of ICMEs from 30 solar radii to 1 AU. We quantitatively characterize this deceleration by the velocity of the upstream ambient solar wind. The effects of varying solar wind parameters on the ICME transit time are quantified and can explain the observed spread in transit times for ICMEs of the same initial velocity. We develop an adjustment formula that can be used in conjunction with other models to reduce the spread in predicted transit times of Earth-directed ICMEs
Ambient solar wind\u27s effect on ICME transit times
[1] Most empirical and numerical models of Interplanetary Coronal Mass Ejection (ICME) propagation use the initial CME velocity as their primary, if not only, observational input. These models generally predict a wide spread of 1 AU transit times for ICMEs with the same initial velocity. We use a 3D coupled MHD model of the corona and heliosphere to determine the ambient solar wind\u27s effect on the propagation of ICMEs from 30 solar radii to 1 AU. We quantitatively characterize this deceleration by the velocity of the upstream ambient solar wind. The effects of varying solar wind parameters on the ICME transit time are quantified and can explain the observed spread in transit times for ICMEs of the same initial velocity. We develop an adjustment formula that can be used in conjunction with other models to reduce the spread in predicted transit times of Earth-directed ICMEs
Verification of real-time WSA-ENLIL+Cone simulations of CME arrival-time at the CCMC from 2010-2016
The Wang-Sheeley-Arge (WSA)-ENLIL+Cone model is used extensively in space
weather operations world-wide to model CME propagation. As such, it is
important to assess its performance. We present validation results of the
WSA-ENLIL+Cone model installed at the Community Coordinated Modeling Center
(CCMC) and executed in real-time by the CCMC space weather team. CCMC uses the
WSA-ENLIL+Cone model to predict CME arrivals at NASA missions throughout the
inner heliosphere. In this work we compare model predicted CME arrival-times to
in-situ ICME leading edge measurements at STEREO-A, STEREO-B, and Earth (Wind
and ACE) for simulations completed between March 2010-December 2016 (over 1,800
CMEs). We report hit, miss, false alarm, and correct rejection statistics for
all three locations. For all predicted CME arrivals, the hit rate is 0.5, and
the false alarm rate is 0.1. For the 273 events where the CME was predicted to
arrive at Earth, STEREO-A, or STEREO-B, and was actually observed (hit event),
the mean absolute arrival-time prediction error was 10.4 +/- 0.9 hours, with a
tendency to early prediction error of -4.0 hours. We show the dependence of the
arrival-time error on CME input parameters. We also explore the impact of the
multi-spacecraft observations used to initialize the model CME inputs by
comparing model verification results before and after the STEREO-B
communication loss (since September 2014) and STEREO-A sidelobe operations
(August 2014-December 2015). There is an increase of 1.7 hours in the CME
arrival time error during single, or limited two-viewpoint periods, compared to
the three-spacecraft viewpoint period. This trend would apply to a future space
weather mission at L5 or L4 as another coronagraph viewpoint to reduce CME
arrival time errors compared to a single L1 viewpoint
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