27 research outputs found
Resonant Control of Interaction Between Different Electronic States
We observe a magnetic Feshbach resonance in a collision between the ground
and metastable states of two-electron atoms of ytterbium (Yb). We measure the
on-site interaction of doubly-occupied sites of an atomic Mott insulator state
in a three-dimensional optical lattice as a collisional frequency shift in a
high-resolution laser spectroscopy. The observed spectra are well fitted by a
simple theoretical formula, in which two particles with an s-wave contact
interaction are confined in a harmonic trap. This analysis reveals a wide
variation of the interaction with a resonance behavior around a magnetic field
of about 1.1 Gauss for the energetically lowest magnetic sublevel of
Yb, as well as around 360 mG for the energetically highest magnetic
sublevel of Yb. The observed Feshbach resonance can only be induced
by an anisotropic inter-atomic interaction. This novel scheme will open the
door to a variety of study using two-electron atoms with tunable interaction.Comment: 5 pages, 5 figure
Laser spectroscopic probing of coexisting superfluid and insulating states of an atomic Bose-Hubbard system
A system of ultracold atoms in an optical lattice has been regarded as an ideal quantum simulator for a Hubbard model with extremely high controllability of the system parameters. While making use of the controllability, a comprehensive measurement across the weakly to strongly interacting regimes in the Hubbard model to discuss the quantum many-body state is still limited. Here we observe a great change in the excitation energy spectra across the two regimes in an atomic Bose–Hubbard system by using a spectroscopic technique, which can resolve the site occupancy in the lattice. By quantitatively comparing the observed spectra and numerical simulations based on sum rule relations and a binary fluid treatment under a finite temperature Gutzwiller approximation, we show that the spectra reflect the coexistence of a delocalized superfluid state and a localized insulating state across the two regimes
Circadian protection against bacterial skin infection by epidermal CXCL14-mediated innate immunity
体内時計は夜間に自然免疫を発動 --皮膚ケモカインによる自然免疫機構--. 京都大学プレスリリース. 2022-06-16.Biological clocks set for skin immunity. 京都大学プレスリリース. 2022-06-21.The epidermis is the outermost layer of the skin and the body’s primary barrier to external pathogens; however, the early epidermal immune response remains to be mechanistically understood. We show that the chemokine CXCL14, produced by epidermal keratinocytes, exhibits robust circadian fluctuations and initiates innate immunity. Clearance of the skin pathogen Staphylococcus aureus in nocturnal mice was associated with CXCL14 expression, which was high during subjective daytime and low at night. In contrast, in marmosets, a diurnal primate, circadian CXCL14 expression was reversed. Rhythmically expressed CXCL14 binds to S. aureus DNA and induces inflammatory cytokine production by activating Toll-like receptor (TLR)9-dependent innate pathways in dendritic cells and macrophages underneath the epidermis. CXCL14 also promoted phagocytosis by macrophages in a TLR9-independent manner. These data indicate that circadian production of the epidermal chemokine CXCL14 rhythmically suppresses skin bacterial proliferation in mammals by activating the innate immune system
Plasmonic Metal Nanostructures Meet Triplet–Triplet Annihilation-Based Photon Upconversion Systems: Performance Improvements and Application Trends
Improving the performance of upconversion systems based on triplet–triplet annihilation (TTA-UC) can have far-reaching implications for various fields, including solar devices, nano-bioimaging, and nanotherapy. This review focuses on the use of localized surface plasmon (LSP) resonance of metal nanostructures to enhance the performance of TTA-UC systems and explores their potential applications. After introducing the basic driving mechanism of TTA-UC and typical sensitizers used in these systems, we discuss recent studies that have utilized new sensitizers with distinct characteristics. Furthermore, we confirm that the enhancement in upconverted emission can be explained, at least in part, by the mechanism of “metal-enhanced fluorescence”, which is attributed to LSP resonance-induced fluorescence enhancement. Next, we describe selected experiments that demonstrate the enhancement in upconverted emission in plasmonic TTA-UC systems, as well as the emerging trends in their application. We present specific examples of studies in which the enhancement in upconverted emission has significantly improved the performance of photocatalysts under both sunlight and indoor lighting. Additionally, we discuss the potential for future developments in plasmonic TTA-UC systems
Quantum Yields of Photoluminescence of TiO<sub>2</sub> Photocatalysts
Here, we determined the quantum yields of photoluminescence
(ΦLumi) of five commercially available TiO2 photocatalysts
(two rutile and three anatase; particle diameter: 7–400 nm)
by comparison with ΦLumi values obtained for three
luminescent inorganic standard materials. The shapes of the luminescence
spectra of the photocatalysts were similar to those reported previously.
Very small ΦLumi values were obtained for all five
photocatalysts [e.g., 5.2 × 10–6 for nano-sized
anatase TiO2 (particle diameter: 7 nm)], indicating that
photoluminescence is a minor channel in the photophysical processes
of these materials. In addition, ΦLumi was much larger
for the photocatalysts with a larger particle size than for those
with a smaller particle size for both anatase and rutile TiO2, which implies that luminescence arises predominantly from the bulk
of the particles and that the surface plays a role as a quenching
center in both polymorphs. The origin of the luminescence is discussed
in relation to the previous studies
Prostaglandin E2 facilitates neurite outgrowth in a motor neuron-like cell line, NSC-34
Prostaglandin E2 (PGE2) exerts various biological effects by binding to E-prostanoid receptors (EP1-4). Although recent studies have shown that PGE2 induces cell differentiation in some neuronal cells such as mouse DRG neurons and sensory neuron-like ND7/23 cells, it is unclear whether PGE2 plays a role in differentiation of motor neurons. In the present study, we investigated the mechanism of PGE2-induced differentiation of motor neurons using NSC-34, a mouse motor neuron-like cell line. Exposure of undifferentiated NSC-34 cells to PGE2 and butaprost, an EP2-selective agonist, resulted in a reduction of MTT reduction activity without increase the number of propidium iodide-positive cells and in an increase in the number of neurite-bearing cells. Sulprostone, an EP1/3 agonist, also significantly lowered MTT reduction activity by 20%; however, no increase in the number of neurite-bearing cells was observed within the concentration range tested. PGE2-induced neurite outgrowth was attenuated significantly in the presence of PF-0441848, an EP2-selective antagonist. Treatment of these cells with dibutyryl-cAMP increased the number of neurite-bearing cells with no effect on cell proliferation. These results suggest that PGE2 promotes neurite outgrowth and suppresses cell proliferation by activating the EP2 subtype, and that the cAMP-signaling pathway is involved in PGE2-induced differentiation of NSC-34 cells. Keywords: Prostaglandin E2, E-prostanoid receptors, Motor neuron, Neurite outgrowth, cAM
Photophysical and Electrochemical Properties of Thienylnaphthalimide Dyes with Excellent Photostability
The development of
robust dyes is a highly important theme for
any applications of dyes. Here we present photophysical and electrochemical
characterization of a set of robust dyes based on the thienylnaphthalimide
unit. The set is comprised of the thienylnaphthalimide derivatives
with phenyl- (Ph-), 4-nitrophenyl- (NO<sub>2</sub>Ph-), and 4-(diphenylamino)phenyl
(Ph<sub>2</sub>NPh-) substituents as exemplars covering electron-withdrawing
to electron-donating groups. The fluorescence quantum yields of the
Ph-TNI increases as the solvent polarity increases, while that of
Ph<sub>2</sub>NPh-TNI showed the opposite trend. Changes in the rates
of nonradiative decay were found to be a major factor for these contrasting
behaviors. Cyclic voltammetry showed that the substituent effects
were more apparent for the HOMO energies rather than the LUMO energies.
Density functional theory calculations showed that the first singlet
excited state of these compounds is a <sup>1</sup>π,π*
state with a significant charge transfer character. Ph-TNI and Ph<sub>2</sub>NPh-TNI are much more stable against photodegradation than
coumarin and fluorescein dyes