6,447 research outputs found
Coherent single-atom superradiance
No full textBuilding up to superradiance, one by one
Superradiance is a quantum phenomenon that occurs when emitters are sufficiently close to change spontaneous emission. Controlling the position and state of emitters within an atomic ensemble, however, is technically challenging. Kim
et al.
show that spatial correlations can be replaced by temporal correlations to achieve superradiance (see the Perspective by Meschede). They dropped prepared atoms into a high-quality optical cavity and found that the number of photons within the cavity built up superradiantly as the atoms dropped through one by one. The method provides a versatile platform for generating nonclassical states of light.
Science
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662
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641
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Water-Ion Interaction Determines the Mobility of Ions in Highly Concentrated Aqueous Electrolytes
No full textSolvation engineering plays a critical role in tailoring the performance of batteries, particularly through the use of highly concentrated electrolytes, which offer heterogeneous solvation structures of mobile ions with distinct electrochemical properties. In this study, we employed spectroscopic techniques and molecular dynamics simulations to investigate mixed-cation (Li+/K+) acetate aqueous electrolytes. Our research unravels the pivotal role of water in facilitating ion transport within a highly viscous medium. Notably, Li+ cations primarily form ion aggregates, predominantly interacting with acetate anions, while K+ cations emerge as the principal charge carriers, which is attributed to their strong interaction with water molecules. Intriguingly, even at a concentration as high as 40 m, a substantial amount of water molecules persistently engages in hydrogen bonding with one another, creating mobile regions rich in K+ ions. Our observations of a redshift of the OH stretching band of water suggest that the strength of the hydrogen bond alone cannot account for the expansion of the electrochemical stability window. These findings offer valuable insights into the cation transfer mechanism, shedding light on the contribution of water-bound cations to both the ion conductivity and the electrochemical stability window of aqueous electrolytes for rechargeable batteries. Our comprehensive molecular-level understanding of the interplay between cations and water provides a foundation for future advances in solvation engineering, leading to the development of high-performance batteries with improved energy storage and safety profiles. © 2024 American Chemical SocietyFALSEsciescopu
Wettability of graphene and interfacial water structure
No full text© 2021 Elsevier Inc.Understanding the wettability of graphene is important for various applications, such as water desalination, energy storage, and catalysis. However, the detailed water hydrogen-bonding structure at the water-graphene interface is not yet fully understood. Using vibrational sum-frequency-generation (VSFG) spectroscopy, we elucidate the water structure at a water-graphene interface. As the number of graphene layers increases, water molecules with dangling OH groups become more populated, indicating the transition from transparency to translucency. We compare the water contact angles on the graphene surfaces with VSFG results, showing an excellent correlation between the water adhesion energy of graphene and the fraction of dangling OH groups estimated from the VSFG spectrum. This observation suggests that the VSFG could be an incisive technique for measuring water's adhesion energy on any spatially confined interface where the water contact angle cannot be measured. We anticipate that the VSFG results will help to elucidate the wettability of low-dimensional materials.11Nsciescopu
Thermodynamic and Transport Properties of H<sub>2</sub>/H<sub>2</sub>O/NaB(OH)<sub>4</sub> Mixtures Using the Delft Force Field (DFF/B(OH)<sub>4</sub><sup>-</sup>)
No full textSodium borohydride (NaBH4) has a high hydrogen (H2 ) gravimetric capacity of 10.7 wt %. NaBH4 releases H2 through a hydrolysis reaction in which aqueous NaB(OH)4 is formed as a byproduct. NaB(OH)4 strongly influences the thermophysical properties of aqueous solutions (i.e., densities, viscosities, and electrical conductivities) and the hydrolysis reaction kinetics and conversion of NaBH4. Here, molecular dynamics (MD) simulations are performed to compute viscosities, electrical conductivities, and self-diffusivities of H2 , Na+, and B(OH)4- for a temperature and concentration range of 298-353 K and 0-5 mol NaB(OH)4/kg water, respectively. Continuous fractional component Monte Carlo (CFCMC) simulations are used to compute the solubilities of H2 and activities of water in aqueous NaB(OH)4 solutions for the same temperature and concentration range. A new force field is developed (Delft force field of B(OH)4-: DFF/B(OH)4-) in which B(OH)4- is modeled as a tetrahedral structure with a scaled charge of −0.85. The OH group in B(OH)4- is modeled as a single interaction site. This force field is based on TIP4P/2005 water and the Madrid-2019 Na+ force field. The MD simulations can accurately capture the densities and viscosities within 2.5% deviation from available experimental data at 298 K up to a concentration of 5 mol NaB(OH)4/kg water. The computed electrical conductivities deviate by ca. 10% from experimental data at 298 K for the same concentration range. Based on the molecular simulations results, engineering equations are developed for shear viscosities, self-diffusivities of H2, Na+, and B(OH)4-, and solubilities of H2, which can be used to design and model NaBH4 hydrolysis reactors.Engineering ThermodynamicsComplex Fluid ProcessingTeam Poulumi De
Oh Holly, The Fish is Dead
No full textFrom Kurt Vonnegut to Stephen King, many novelists use metanarrative techniques to insert fictional versions of themselves in the stories they tell. The function of deploying such techniques is often to draw attention to the liminal space between the fictional constructs inherent in the novel as a form, and the real world from which the constructs draw inspiration, and indeed, are read by an audience. For emerging writers working in short form narratives, however, the structural demands of the short story or flash fiction make the use of similar techniques problematic in the level of depth to which they can be deployed.\ud
\ud
‘Oh Holly, the fish is dead’ is the fourth in a series of short stories that work to overcome the structural limitations of a succinct form by developing a fractured fictional version of the author over a number of pieces and published across a range of sites. The accumulative affect is a richer metanarrative textual arrangement that also allows for the individual short stories to function independently
Continuous Hamiltonian dynamics and area-preserving homeomorphism group of D2
No full textThe main purpose of this paper is to propose a scheme of a proof of the nonsimpleness of the group {\rm Homeo}^\Omega(D^2,\del D^2) of area preserving homeomorphisms of the 2-disc . We first establish the existence of Alexander isotopy in the category of Hamiltonian homeomorphisms. This reduces the question of extendability of the well-known Calabi homomorphism \Cal: {\rm Diff}^\Omega(D^1,\del D^2) \to \R to a homomorphism \overline \Cal: {\rm Hameo(}D^2,\del D^2) \to \R to that of the vanishing of the basic phase function , a Floer theoretic graph selector constructed in \cite{oh:jdg}, that is associated to the graph of the topological Hamiltonian loop and its normalized Hamiltonian on that is obtained via the natural embedding . Here {\rm Hameo(}D^2,\del D^2) is the group of Hamiltonian homeomorphisms introduced by M\"uller and the author \cite{oh:hameo1}. We then provide an evidence of this vanishing conjecture by proving the conjecture for the special class of \emph{weakly graphical} topological Hamiltonian loops on via a study of the associated Hamiton-Jacobi equation.1111Ysciescopuskc
Asarum chungbuensis B. U. Oh. Since 2005
No full textAsarum chungbuensis (C.S. Yook & J.G. Kim) B.U. Oh (2005: 24) Basionym: Asiasarum sieboldii Miq. f. chungbuensis C.S. Yook & J.G. Kim (1996: 343) Type (neotype, designated here):— KOREA. Gyeonggi-do: Pocheon-si, Mt. Gwangdeoksan, 294 m, 38°04′51″N, 127°25′18″E, 27 April 2020, H. D.Jang & G. H. Nam 506 (KB! barcode NIBRVP774931)(Fig. 1). Notes: —Regarding the scientific name of this taxon, Yamaki (Feb. 1996) published the name of Asiasarum sieboldii (Miq.) F. Maek. var. versicolor (1996: 1), and Yook & Kim (Nov. 1996) published the name of Asiasarum sieboldii (Miq.) F. Maek. f. chungbuensis in the same year. Later, Lee & Lee (2000) republished it with a new combination name Asarum versicolor (Yamaki) Y.N. Lee (2000: 19). Oh et al. (2005) made a new combination name Asarum chungbuensis (C.S. Yook & J.G. Kim) B.U. Oh. Since then, A. versicolor (Yamaki) Y.N. Lee has been accepted as the legitimate name, having priority (Yamaji et al. 2007, So & Kim 2008, Oh 2008, National Institute of Biological Resources 2011). In contrast, A. chungbuensis (C.S. Yook & J.G. Kim) B.U. Oh has been treated as a superfluous name of A. versicolor. However, we detected problems regarding the scientific name A. versicolor (Yamaki) Y.N. Lee. Lee (2000) referred to the basionym as “ Asiasarum sieboldii Miq. var. versicolor Yamaki, J. Jap. Bot. 71: 1–10, 1995”; thus, the name has not been validly published because whole pages of the protologue have been cited. According to Article 41.5 of the ICN (Turland et al. 2018), a new combination name is not validly published unless its basionym is clearly indicated, and a full and direct reference is given to its author and place of valid publication, with page or plate reference and date on or after January 1, 1953. In addition, according to Article 11.2 of the ICN, although Asiasarum sieboldii var. versicolor Yamaki was published before A. sieboldii f. chungbuensis C.S. Yook & J.G. Kim, neither of these names have any priority outside the rank at which they were published. Consequently, A. versicolor (Yamaki) Y.N. Lee is unacceptable, and A. chungbuensis (C.S. Yook & J.G. Kim) B.U. Oh is accepted as the legitimate name of this taxon.Published as part of Jang, Hyun-Do, Nam, Gi-Heum, Oh, Hyun-Kyung & Leem, Hyosun, 2021, Typification of the names Asarum chungbuensis and A. maculatum (Aristolochiaceae), pp. 295-299 in Phytotaxa 508 (3) on page 298, DOI: 10.11646/phytotaxa.508.3.5, http://zenodo.org/record/542599
Serum 25-hydroxyvitamin D and cognitive decline in the very old: The Newcastle 85+ study
No full textBackground and purpose:
Studies investigating the association between 25-hydroxyvitamin D [25(OH)D] and cognition in the very old (85+) are lacking.
Methods:
Cross-sectional (baseline) and prospective data (up to 3 years follow-up) from 775 participants in the Newcastle 85+ Study were analysed for global (measured by the Standardized Mini-Mental State Examination) and attention-specific (measured by the attention battery of the Cognitive Drug Research test) cognitive performance in relation to season-specific 25(OH)D quartiles.
Results:
Those in the lowest and highest season-specific 25(OH)D quartiles had an increased risk of impaired prevalent (1.66, 95% confidence interval 1.06–2.60, P = 0.03; 1.62, 95% confidence interval 1.02–2.59, P = 0.04, respectively) but not incident global cognitive functioning or decline in functioning compared with those in the middle quartiles adjusted for sociodemographic, health and lifestyle confounders. Random effects models showed that participants belonging to the lowest and highest 25(OH)D quartiles, compared with those in the middle quartiles, had overall slower (log-transformed) attention reaction times for Choice Reaction Time (lowest, b = 0.023, P = 0.01; highest, b = 0.021, P = 0.02), Digit Vigilance Task (lowest, b = 0.009, P = 0.05; highest,b = 0.01, P = 0.02) and Power of Attention (lowest, b = 0.017, P = 0.02;highest, b = 0.022, P = 0.002) and greater Reaction Time Variability (lowest,b = 0.021, P = 0.02; highest, b = 0.02, P = 0.03). The increased risk of worse global cognition and attention amongst those in the highest quartile was not observed in non-users of vitamin D supplements/medication.
Conclusion:
Low and high season-specific 25(OH)D quartiles were associated with prevalent cognitive impairment and poorer overall performance in attention-specific tasks over 3 years in the very old, but not with global cognitive decline or incident impairment
Volume 10, Number 27
No full textThis is an 8-page weekly magazine for children in Catholic religious education. Pages 6-7 are given to "Gospel Activity." Six cartoon panels are filled with black-and-white line drawings. Pupils are urged to draw in the last two empty panels. The story is presented as "The Porcupine and the Moles" telling one of Aesop's fables. Porcupine asks the moles if he could share their cave for the winter, and the welcome him. After a week, the moles are suffering from the porcupine's needles. They decide to talk with the porcupine and ask him to leave. "Oh, no! This place suits me well." Pupils are asked to talk through with each other how the porcupine and moles can solve their problem. Five questions help. They are to write or draw their group's solution into the two empty panels. I would say that this is a good challenge. Mom wrote on a post-it note "I wish you could have heard the solutions my students gave to this problem."No Autho
Wettability of graphene, water contact angle, and interfacial water structure
No full text© 2022 Elsevier Inc.Understanding the details of water interacting with graphene is essential for various applications, such as water desalination, energy storage, and catalysis. However, the hydrogen-bonding structure of the water at the graphene-water interface has not been fully understood. Vibrational sum frequency generation (VSFG) spectroscopy is suited to elucidate the water structure at graphene-water interfaces. With varying numbers of graphene layers or tuning the doping level of a single monolayer, the interfacial water structure differs substantially. Specifically, as the number of graphene layers increases, water molecules with non-H-bonded, dangling OH groups become increasingly apparent. The fraction of dangling OH groups inferred from the VSFG spectrum correlates with the water adhesion energy of graphene. This observation suggests that VSFG could be an incisive technique for measuring the water adhesion energy on any spatially confined interface where the water contact angle cannot be measured. We anticipate that VSFG spectroscopy will shed light on the wettability of low-dimensional materials.11Nsciescopu
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