Stroboscopic visualization of nuclear or electron dynamics in atoms, molecules or solids requires ultrafast pump and probe pulses and a close to perfect synchronization between the two. We have ...developed a 3 MeV ultrafast electron diffraction (UED) probe technology that nominally reduces the electron bunch duration and the arrival time jitter to the subfemtosecond level. This simple configuration uses a radiofrequency photogun and a 90° achromatic bend and is designed to provide effectively jitter-free conditions. Terahertz streaking measurements reveal an electron bunch duration of 25 fs, even for a charge as high as 0.6 pC, and an arrival time jitter of 7.8 fs, the latter limited by only the measurement accuracy. From pump–probe measurements of photoexcited bismuth films, the instrument response function was determined to be 31 fs. This pioneering jitter-free technique paves the way towards UED of attosecond phenomena in atomic, molecular and solid-state dynamics.An ultrafast electron diffraction facility with an overall temporal resolution of 31 fs root mean square is developed. Even for a charge as high as 0.6 pC, the electron bunch duration and timing jitter are 25 fs and less than 10 fs, respectively.
Abstract
The deflection of charged particles is an intuitive way to visualize an electromagnetic oscillation of coherent light. Here, we present a real-time ultrafast oscilloscope for time-frozen ...visualization of a terahertz (THz) optical wave by probing light-driven motion of relativistic electrons. We found the unique condition of subwavelength metal slit waveguide for preserving the distortion-free optical waveform during its propagation. Momentary stamping of the wave, transversely travelling inside a metal slit, on an ultrashort wide electron bunch enables the single-shot recording of an ultrafast optical waveform. As a proof-of-concept experiment, we successfully demonstrated to capture the entire field oscillation of a THz pulse with a sampling rate of 75.7 TS/s. Owing to the use of transversely-wide and longitudinally-short electron bunch and transversely travelling wave, the proposed “single-shot oscilloscope” will open up new avenue for developing the real-time petahertz (PHz) metrology.
Abstract
We analyze the very short Einstein timescale (
t
E
≃ 7 hr) event KMT-2019-BLG-2073. Making use of the pronounced finite-source effects generated by the clump giant source, we measure the ...Einstein radius
θ
E
≃ 4.8
μ
as and so infer a mass
M
=
59
M
⊕
(
π
rel
/
16
μ
as
)
−
1
, where
π
rel
is the lens-source relative parallax. We find no significant evidence for a host of this planetary-mass object, though one could be present at sufficiently wide separation. If so, it would be detectable after about 10 yr. This is the fourth isolated microlens with a measured Einstein radius
θ
E
< 10
μ
as, which we argue is a useful threshold for a “likely free-floating planet (FFP)” candidate. We outline a new approach to constructing a homogeneous sample of giant-star finite-source/point-lens (FSPL) events, within which the subsample of FFP candidates can be statistically analyzed. We illustrate this approach using 2019 KMTNet data and show that there appears to be a large
θ
E
gap between the two FFP candidates and the 11 other FSPL events. We argue that such sharp features are more identifiable in a sample selected on
θ
E
compared to the traditional approach of identifying candidates based on short
t
E
.
The most practical way of storing hydrogen gas for fuel cell vehicles is to use a composite overwrapped pressure vessel. Depending on the driving distance range and power requirement of the vehicles, ...there can be various operational pressure and volume capacity of the tanks, ranging from passenger vehicles to heavy-duty trucks. The current commercial hydrogen storage method for vehicles involves storing compressed hydrogen gas in high-pressure tanks at pressures of 700 bar for passenger vehicles and 350 bar to 700 bar for heavy-duty trucks. In particular, hydrogen is stored in rapidly refillable onboard tanks, meeting the driving range needs of heavy-duty applications, such as regional and line-haul trucking. One of the most important factors for fuel cell vehicles to be successful is their cost-effectiveness. So, in this review, the cost analysis including the process analysis, raw materials, and manufacturing processes is reviewed. It aims to contribute to the optimization of both the cost and performance of compressed hydrogen storage tanks for various applications.
Abstract
We inaugurate a program of “mass production” of microlensing planets discovered in 2021 KMTNet data, with the aim of laying the basis for future statistical studies. While we ultimately plan ...to quickly publish all 2021 planets meeting some minimal criteria, the current sample of four was chosen simply on the basis of having low initial estimates of the planet–host mass ratio,
q
. It is therefore notable that two members of this sample suffer from a degeneracy in the normalized source radius
ρ
that arises from different morphologies of closely spaced caustics. All four planets (KMT-2021-BLG-1391, KMT-2021-BLG-1253, KMT-2021-BLG-1372, KMT-2021-BLG-0748) have well-characterized mass ratios,
q
, and therefore are suitable for mass-ratio frequency studies. Both of the
ρ
degeneracies can be resolved by future adaptive optics (AO) observations on 30 m class telescopes. We provide general guidance for such AO observations for all events in anticipation of the prospect that they will revolutionize the field of microlensing planets.
Aims.
We announce the discovery of a microlensing planetary system, in which a sub-Saturn planet is orbiting an ultracool dwarf host.
Methods.
We detected the planetary system by analyzing the ...short-timescale (
t
E
~ 4.4 days) lensing event KMT-2018-BLG-0748. The central part of the light curve exhibits asymmetry due to negative deviations in the rising side and positive deviations in the falling side.
Results.
We find that the deviations are explained by a binary-lens model with a mass ratio between the lens components of
q
~ 2 × 10
−3
. The short event timescale, together with the small angular Einstein radius,
θ
E
~ 0.11 mas, indicate that the mass of the planet host is very small. The Bayesian analysis conducted under the assumption that the planet frequency is independent of the host mass indicates that the mass of the planet is
M
p
= 0.18
−0.10
+0.29
M
J
, and the mass of the host,
M
h
= 0.087
−0.047
+0.138
M
⊙
, is near the star–brown dwarf boundary, but the estimated host mass is sensitive to this assumption about the planet hosting probability. High-resolution follow-up observations would lead to revealing the nature of the planet host.
Abstract
We complete the analysis of all 2018 sub-prime-field microlensing planets identified by the KMTNet AnomalyFinder. Among the 9 previously unpublished events with clear planetary solutions, 6 ...are clearly planetary (OGLE-2018-BLG-0298, KMT-2018-BLG-0087, KMT-2018-BLG-0247, KMT-2018-BLG-0030, OGLE-2018-BLG-1119, and KMT-2018-BLG-2602), while the remaining 3 are ambiguous in nature. The above ordering of these events is made to facilitate grouping of their Bayesian estimates: the first two are lower-mass gas giants while the last four are Jovian-class planets; the first three most likely lie in the bulge, the last in the disk, and the remaining two are equally likely to be in either population. More specifically, these six planets have host masses
M
host
=
(
0.69
−
0.30
+
0.34
,
0.10
−
0.05
+
0.14
,
0.29
−
0.14
+
0.28
,
0.51
−
0.31
+
0.43
,
0.48
−
0.28
+
0.35
,
0.66
−
0.36
+
0.42
)
M
⊙
, planet masses
M
planet
=
(
0.14
−
0.06
+
0.07
,
0.23
−
0.12
+
0.32
,
2.11
−
1.04
+
2.09
,
1.45
−
0.88
+
1.23
,
0.91
−
0.52
+
0.66
,
1.15
−
0.63
+
0.73
)
M
Jup
, and distances
D
L
=
(
6.54
−
1.23
+
0.95
,
7.02
−
1.15
+
1.03
,
6.76
−
1.24
+
0.99
,
6.48
−
1.96
+
1.28
,
5.76
−
2.48
+
1.43
,
4.31
−
1.84
+
1.97
)
kpc
. In addition, there are 8 previously published sub-prime-field planets that were selected by the AnomalyFinder algorithm. Together with a companion paper on 2018 prime-field planets, this work lays the basis for comprehensive statistical studies. We carry out two such studies, one on caustic topologies and the other on the role of Gaia data. From the first, as expected, half (17/33) of the 2018 planets likely to enter the mass-ratio analysis have non-caustic-crossing anomalies. However, only 1 of the 5 noncaustic anomalies with planet-host mass ratio
q
< 10
−3
was discovered by eye (compared to 7 of the 12 with
q
> 10
−3
), showing the importance of the semiautomated AnomalyFinder search. From the second, we find that Gaia has played a major role in the interpretation of 16% of the sample and a supplementary role in 6%.
Aims
The impact of donor abdominal fat‐to‐muscle ratio (FMR) on kidney transplant (KT) outcomes was assessed. Given the transient nature of the donor's metabolic environment in transplant recipients, ...this study investigated the capacity of body composition to induce metabolic memory effects.
Materials and Methods
KT patients (n = 895) who received allografts from living donors (2003–2013) were included. Donor fat and muscle were quantified using pre‐KT abdominal computed tomography scans. Patients were categorised into donor FMR tertiles and followed up for graft outcomes. Additionally, genome‐wide DNA methylation analysis was performed on 28 kidney graft samples from KT patients in the low‐ and high‐FMR groups.
Results
Mean recipient age was 42.9 ± 11.4 years and 60.9% were males. Donor FMR averaged 1.67 ± 0.79. Over a median of 120.9 ± 42.5 months, graft failure (n = 127) and death‐censored graft failure (n = 109) were more frequent in the higher FMR tertiles. Adjusted hazard ratios for the highest versus lowest FMR tertile were 1.71 (95% CI, 1.06–2.75) for overall graft failure and 1.90 (95% CI, 1.13–3.20) for death‐censored graft failure. Genome‐wide DNA methylation analysis identified 58 differentially methylated regions (p < 0.05, |Δβ| > 0.2) and 35 genes showed differential methylation between the high‐ (FMR >1.91) and low‐FMR (FMR <1.27) groups.
Conclusions
Donors with increased fat and reduced muscle composition may negatively impact kidney allograft survival in recipients, possibly through the transmission of epigenetic changes, implying a body‐composition‐related metabolic memory effect.
Ultrafast electron diffraction (UED) has evolved to be a powerful tool for the study of structural dynamics with subpicosecond temporal resolution and subatomic spatial resolution. Recently, there ...have been intense research efforts toward femtosecond timing jitter and stability for improving the temporal resolution of UEDs, however, so far there has been no work showing long‐term (e.g., >1 h) stable timing for MeV‐level UED systems. In this article, a comprehensive timing synchronization method, based on optical‐radiofrequency synchronization and THz streaking, is demonstrated to maintain sub‐10‐fs long‐term timing stability for radiofrequency‐gun‐based MeV‐level UED, which results in 5.5 fs root‐mean‐square timing drift maintained over 4600 s. With high electron energy and low timing drift, the demonstrated capability is an important step toward studying ultrafast phenomena in samples with low scattering power, such as volatile gases and 2D materials.
A THz‐streaking based timing system with sub‐10‐fs stability is implemented to operate MeV‐class ultrafast electron diffraction apparatus. Various timing methodologies, such as radiofrequency‐to‐laser synchronization, optical timing monitoring, electron dispersion control, are applied to enable THz‐streaking with few femtosecond resolution. With the THz‐driven streak camera, timing of ultrafast electron bunch is stabilized to 5.5 fs in rms.
In this paper, we report the structural dynamics of polycrystalline bismuth (Bi) thin films in response to photoexcitation, visualized by mega-electron-volt ultrafast electron diffraction. The data ...reveal that the carrier–phonon scattering process involves phonon squeezing within sub-picoseconds (ps) and lattice thermalization within a few ps. Through the time-resolved pair distribution function analysis, we directly observe the changes in the interatomic distance of adjacent Bi atoms in real space, which can be explained by phonon softening and subsequent phonon squeezing.
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