93 research outputs found
First constraint on cosmological variation of the proton-to-electron mass ratio from two independent telescopes
A high signal-to-noise spectrum covering the largest number of hydrogen lines
(90 H2 lines and 6 HD lines) in a high redshift object was analyzed from an
observation along the sight-line to the bright quasar source J2123005 with
the UVES spectrograph on the ESO Very Large Telescope (Paranal, Chile). This
delivers a constraint on a possible variation of the proton-to-electron mass
ratio of Dmu/mu = (8.5 \pm 3.6_{stat} \pm 2.2_{syst}) x 10^{-6} at redshift
z=2.059$, which agrees well with a recently published result on the same system
observed at the Keck telescope yielding Dmu/mu = (5.6 \pm 5.5_{stat} \pm
2.9_{syst}) x 10^{-6}. Both analyses used the same robust absorption line
fitting procedures with detailed consideration of systematic errors.Comment: Accepte
A scanning tunneling microscope capable of electron spin resonance and pump-probe spectroscopy at mK temperature and in vector magnetic field
In the last decade, detecting spin dynamics at the atomic scale has been
enabled by combining techniques like electron spin resonance (ESR) or
pump-probe spectroscopy with scanning tunneling microscopy (STM). Here, we
demonstrate an ultra-high vacuum (UHV) STM operational at milliKelvin (mK) and
in a vector magnetic field capable of both ESR and pump-probe spectroscopy. By
implementing GHz compatible cabling, we achieve appreciable RF amplitudes at
the junction while maintaining mK base temperature. We demonstrate the
successful operation of our setup by utilizing two experimental ESR modes
(frequency sweep and magnetic field sweep) on an individual TiH molecule on
MgO/Ag(100) and extract the effective g-factor. We trace the ESR transitions
down to MHz into an unprecedented low frequency band enabled by the mK base
temperature. We also implement an all-electrical pump-probe scheme based on
waveform sequencing suited for studying dynamics down to the nanoseconds range.
We benchmark our system by detecting the spin relaxation time T1 of individual
Fe atoms on MgO/Ag(100) and note a field strength and orientation dependent
relaxation time
Constraining the variation of fundamental constants at z ~ 1.3 using 21-cm absorbers
We present high resolution optical spectra obtained with the Ultraviolet and
Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) and 21-cm
absorption spectra obtained with the Giant Metrewave Radio Telescope (GMRT) and
the Green Bank Telescope (GBT) of five quasars along the line of sight of which
21-cm absorption systems at 1.17 < z < 1.56 have been detected previously. We
also present milliarcsec scale radio images of these quasars obtained with the
Very Large Baseline Array (VLBA). We use the data on four of these systems to
constrain the time variation of x = g_p*alpha^2/mu where g_p is the proton
gyromagnetic factor, alpha is the fine structure constant, and mu is the
proton-to-electron mass ratio. We carefully evaluate the systematic
uncertainties in redshift measurements using cross-correlation analysis and
repeated Voigt profile fitting. In two cases we also confirm our results by
analysing optical spectra obtained with the Keck telescope. We find the
weighted and the simple means of Delta_x / x to be respectively -(0.1 +/-
1.3)x10^-6 and (0.0 +/- 1.5)x10^-6 at the mean redshift of = 1.36
corresponding to a look back time of ~ 9 Gyr. This is the most stringent
constraint ever obtained on Delta_x / x. If we only use the two systems towards
quasars unresolved at milliarcsec scales, we get the simple mean of Delta_x / x
= + (0.2 +/- 1.6)x10^-6. Assuming constancy of other constants we get
Delta_alpha / alpha = (0.0 +/- 0.8)x10^-6 which is a factor of two better than
the best constraints obtained so far using the Many Multiplet Method. On the
other hand assuming alpha and g_p have not varied we derive Delta_mmu / mu =
(0.0 +/- 1.5)x10^-6 which is again the best limit ever obtained on the
variation of mu over this redshift range. [Abridged]Comment: 22 pages, 15 figures, Accepted for publication in MNRA
Quantifying the interplay between fine structure and geometry of an individual molecule on a surface
The pathway toward the tailored synthesis of materials starts with precise characterization of the conformational properties and dynamics of individual molecules. Electron spin resonance (ESR)-based scanning tunneling microscopy can potentially address molecular structure with unprecedented resolution. Here, we determine the fine structure and geometry of an individual titanium-hydride molecule, utilizing a combination of a newly developed millikelvin ESR scanning tunneling microscope in a vector magnetic field and ab initio approaches. We demonstrate a strikingly large anisotropy of the g tensor, unusual for a spin doublet ground state, resulting from a nontrivial orbital angular momentum stemming from the molecular ground state. We quantify the relationship between the resultant fine structure, hindered rotational modes, and orbital excitations. Our model system provides avenues to determine the structure and dynamics of individual molecules. © 2021 American Physical Society.We acknowledge funding from the Dutch Research Council (NWO), and the Vidi Project “Manipulating the interplay between superconductivity and chiral magnetism at the single-atom level” with Project No. 680-47-534. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (SPINAPSE: Grant Agreement No. 818399). F.D.N. thanks the Swiss National Science Foundation for financial support under Grant No. PP00P2_176866. The work of D.I.B., A.N.R. and V.V.M. was supported by Act 211 Government of the Russian Federation Contract No. 02.A03.21.0006
Search for varying constants of nature from astronomical observation of molecules
The status of searches for possible variation in the constants of nature from
astronomical observation of molecules is reviewed, focusing on the
dimensionless constant representing the proton-electron mass ratio
. The optical detection of H and CO molecules with large
ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as
the detection of H with the Cosmic Origins Spectrograph aboard the Hubble
Space Telescope is discussed in the context of varying constants, and in
connection to different theoretical scenarios. Radio astronomy provides an
alternative search strategy bearing the advantage that molecules as NH
(ammonia) and CHOH (methanol) can be used, which are much more sensitive to
a varying than diatomic molecules. Current constraints are
for redshift , corresponding to
look-back times of 10-12.5 Gyrs, and for
, corresponding to half the age of the Universe (both at 3
statistical significance). Existing bottlenecks and prospects for future
improvement with novel instrumentation are discussed.Comment: Contribution to Workshop "High Performance Clocks in Space" at the
International Space Science Institute, Bern 201
A Review of Drowning Prevention Interventions for Children and Young People in High, Low and Middle Income Countries.
Globally, drowning is one of the ten leading causes of child mortality. Children aged <5 years are particularly at risk, and children and young people continue to be overrepresented in drowning statistics. Accordingly, evidence informed interventions to prevent children drowning are of global importance. This review aimed to identify, assess and analyse public health interventions to reduce child drowning and investigate the use of behavioural theories and evaluation frameworks to guide child drowning prevention. Thirteen databases were searched for relevant peer reviewed articles. The systematic review was guided by the PRISMA criteria and registered with PROSPERO. Fifteen articles were included in the final review. Studies were delivered in high, middle and low income countries. Intervention designs varied, one-third of studies targeted children under five. Almost half of the studies relied on education and information to reduce drowning deaths, only three studies used a multi-strategy approach. Minimal use of behavioural theories and/or frameworks was found and just one-third of the studies described formative evaluation. This review reveals an over reliance on education and information as a strategy to prevent drowning, despite evidence for comprehensive multi-strategy approaches. Accordingly, interventions must be supported that use a range of strategies, are shaped by theory and planning and evaluation frameworks, and are robust in intervention design, delivery and evaluation methodology. This approach will provide sound evidence that can be disseminated to inform future practice and policy for drowning prevention
Improving the hyperpolarization of (31)p nuclei by synthetic design
Traditional (31)P NMR or MRI measurements suffer from low sensitivity relative to (1)H detection and consequently require longer scan times. We show here that hyperpolarization of (31)P nuclei through reversible interactions with parahydrogen can deliver substantial signal enhancements in a range of regioisomeric phosphonate esters containing a heteroaromatic motif which were synthesized in order to identify the optimum molecular scaffold for polarization transfer. A 3588-fold (31)P signal enhancement (2.34% polarization) was returned for a partially deuterated pyridyl substituted phosphonate ester. This hyperpolarization level is sufficient to allow single scan (31)P MR images of a phantom to be recorded at a 9.4 T observation field in seconds that have signal-to-noise ratios of up to 94.4 when the analyte concentration is 10 mM. In contrast, a 12 h 2048 scan measurement under standard conditions yields a signal-to-noise ratio of just 11.4. (31)P-hyperpolarized images are also reported from a 7 T preclinical scanner
Strategies for the hyperpolarization of acetonitrile and related Ligands by SABRE
(Chemical Equation Presented) We report on a strategy for using SABRE (signal amplification by reversible exchange) for polarizing 1H and 13C nuclei of weakly interacting ligands which possess biologically relevant and nonaromatic motifs. We first demonstrate this via the polarization of acetonitrile, using Ir(IMes)(COD)Cl as the catalyst precursor, and confirm that the route to hyperpolarization transfer is via the J-coupling network. We extend this work to the polarization of propionitrile, benzylnitrile, benzonitrile, and trans-3-hexenedinitrile in order to assess its generality. In the 1H NMR spectrum, the signal for acetonitrile is enhanced 8-fold over its thermal counterpart when [Ir(H)2(IMes)(MeCN)3]+ is the catalyst. Upon addition of pyridine or pyridine-d5, the active catalyst changes to [Ir(H)2(IMes)- (py)2(MeCN)]+ and the resulting acetonitrile 1H signal enhancement increases to 20- and 60-fold, respectively. In 13C NMR studies, polarization transfers optimally to the quaternary 13C nucleus of MeCN while the methyl 13C is hardly polarized. Transfer to 13C is shown to occur first via the 1H - 1H coupling between the hydrides and the methyl protons and then via either the 2J or 1J couplings to the respective 13Cs, of which the 2J route is more efficient. These experimental results are rationalized through a theoretical treatment which shows excellent agreement with experiment. In the case of MeCN, longitudinal two-spin orders between pairs of 1H nuclei in the three-spin methyl group are created. Two-spin order states, between the 1H and 13C nuclei, are also created, and their existence is confirmed for Me13CN in both the 1H and 13C NMR spectra using the Only Parahydrogen Spectroscopy protocol
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