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Tefillin are Jewish ritual artifacts consisting of leather cases, containing inscribed slips, which are affixed with leather straps to the body of the tefillin practitioner. According to current Jewish ritual law, the tefillin cases and straps are to be colored black. The present study examines seventeen ancient tefillin cases discovered among the Dead Sea Scrolls in caves in the Judean Desert. All seventeen cases display grain surfaces with a very dark, nearly black appearance. We start with a hypothesis that the cases were intentionally colored black in antiquity using either a carbon-based or iron-gall-based paint or dye. The aim of this study is to test this hypothesis by subjecting these tefillin cases to a battery of examinations to assess the presence of carbon and iron used as pigments, and of organic materials which may have been used as binding agents in a paint. The tests deployed are: (1) macroscopic and microscopic analyses; (2) multispectral imaging using infrared wavelengths; (3) Raman spectroscopy; (4) Fourier transform infrared spectroscopy (FTIR); and (5) scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectroscopy. The results of these tests found no traces of carbon-based or iron-gall-based pigments, nor of organic compounds which may have served as binders in a paint. These results suggest that our posited hypothesis is unlikely. Instead, results of the SEM examination suggest it more likely that the black color on the surfaces of the tefillin cases is the result of natural degradation of the leather through gelatinization. The Judean Desert tefillin likely represent tefillin practices prior to when the rabbinic prescription on blackening tefillin was widely practiced. Our study suggests that the kind of non-blackened tefillin which the later rabbis rejected in their own times may well have been quite common in earlier times. [ABSTRACT FROM AUTHOR]

Many animals exhibit remarkable colors that are produced by the constructive interference of light reflected from arrays of intracellular guanine crystals. These animals can fine-tune their crystal-based structural colors to communicate with each other, regulate body temperature, and create camouflage. While it is known that these changes in color are caused by changes in the angle of the crystal arrays relative to incident light, the cellular machinery that drives color change is not understood. Here, using a combination of 3D focused ion beam scanning electron microscopy (FIB-SEM), micro-focused X-ray diffraction, superresolution fluorescence light microscopy, and pharmacological perturbations, we characterized the dynamics and 3D cellular reorganization of crystal arrays within zebrafish iridophores during norepinephrine (NE)-induced color change. We found that color change results from a coordinated 20° tilting of the intracellular crystals, which alters both crystal packing and the angle at which impinging light hits the crystals. Importantly, addition of the dynein inhibitor dynapyrazole-a completely blocked this NE-induced red shift by hindering crystal dynamics upon NE addition. FIB-SEM and microtubule organizing center (MTOC) mapping showed that microtubules arise from two MTOCs located near the poles of the iridophore and run parallel to, and in between, individual crystals. This suggests that dynein drives crystal angle change in response to NE by binding to the limiting membrane surrounding individual crystals and walking toward microtubule minus ends. Finally, we found that intracellular cAMP regulates the color change process. Together, our results provide mechanistic insight into the cellular machinery that drives structural color change. [ABSTRACT FROM AUTHOR]

The sixth-generation wireless communication (6G) extends the electromagnetic pollution up to the terahertz band. The two-dimensional titanium carbide of intercalated structure Ti3C2Tx MXene attracts much attention because it exhibits high terahertz electromagnetic interference (EMI) shielding effectiveness (SE) due to the large intrinsic electrical conductivity as well as few-atom monosheet thickness. Scientists worldwide are making continuous efforts to optimize the MXene structures for EMI shielding application. Innovatively, we demonstrate a chemical method to bend the nanoflake by grafting two types of alkane, octane (C8H18) and dodecane (C12H26), onto the surface terminals. The chain length of alkane exceeds the bond length of surface functionalities Tx (=O, −OH, −F) to introduce intrananoflake and internanoflake strains into Ti3C2Tx MXene. The nanoflake's deformation leads to Raman peak redshift and broader line width. The element distribution shows that the alkane increases the oxygen–fluorine ratio of Ti3C2Tx MXene from 3:2 to 3:1 (Ti3C2Tx-C8H18) and even up to 4:1 (Ti3C2Tx-C12H26). Electronic microscopy (SEM/TEM) shows obvious edge-fold and tensile/compressive deformation of the nanoflake. The EMI SE of Ti3C2Tx-C12H26 achieves 35 dB, which is higher than those of Ti3C2Tx-C8H18 (26 dB) and Ti3C2Tx MXene (22 dB). The alkane grafting increases the absorption coefficient of the MXene thin film by more than 50% but has negligible contribution to the refractive index. Meanwhile, the conductivity of Ti3C2Tx-C8H18 MXene is over twice higher than that of Ti3C2Tx MXene, whereas the conductivity of Ti3C2Tx-C12H26 is three times higher than that of Ti3C2Tx MXene. The nanoflake curvature of alkane grafted Ti3C2Tx MXene enlarges the specific surface area and causes topological defects, which increase the absorption as well as the conductivity so that the terahertz EMI SE is enhanced correspondingly. The realization of Ti3C2Tx MXene of curved nanoflake for the enhancement of terahertz EMI SE is valuable for 6G electromagnetic protection. [ABSTRACT FROM AUTHOR]

While individual single‐wall carbon nanotubes (SWCNTs) have remarkable strength and electrical conductivity, SWCNT networks fabricated from dispersions have inferior properties due to nanotube bundling, limiting the potential applications of SWCNT materials. Herein, a common dye molecule (purpurin) is used to exfoliate SWCNTs via noncovalent functionalization and to fabricate SWCNT materials by a simple solution‐based process. The advantageous noncovalent interactions result in efficient exfoliation and metallic SWCNT enrichment, affording SWCNT materials with high mechanical robustness and electrical conductivity. This method is used to prepare mechanically robust SWCNT films and flexible transparent conductive electrodes. [ABSTRACT FROM AUTHOR]

We examined lithic artifacts from the late Neanderthal site Sesselfelsgrotte (Bavaria, Germany) in order to evaluate the possibility of fire use and intentional flint heat treatment performed by late Neanderthals. We analyzed 1113 flint pieces from the G-layer complex (~60 to 45 kya; Micoquian) and 946 from the lower-layer complex (~115 to 70 kya; Mousterian). Based on macroscopic traits associated with the exposure of flint to heat and fire, we assigned artifacts to one of three groups: burnt, unburnt, and possibly intentionally heated. Our results show that while both complexes demonstrate the clear presence of fire, fire is more common in the younger G-layer complex. Moreover, possibly intentionally heated pieces are significantly more frequent in the G-layer complex, especially among the tools and specifically among side scrapers, suggesting a link between heat treatment and the production of these tools, most probably due to their functional and cultural significance. We therefore suggest that the flint in the G-layer complex of Sesselfelsgrotte underwent intentional heat treatment. The proportions of burnt flint artifacts in both complexes suggest an intensification in fire use at the site over time, while the appearance of possibly intentionally heated artifacts in the G-layer complex suggests the development of this advanced pyrotechnology by Neanderthals sometime between these two timeframes. Our results are supported by sedimentological and faunal data. We view these results as further indication of the advanced cognitive and technological capabilities of Neanderthals, which did not fall short of those of early modern humans. [ABSTRACT FROM AUTHOR]

Many animals undergo changes in functional colors during development, requiring the replacement of integument or pigment cells. A classic example of defensive color switching is found in hatchling lizards, which use conspicuous tail colors to deflect predator attacks away from vital organs. These tail colors usually fade to concealing colors during ontogeny. Here, we show that the ontogenetic blue-to-brown tail color change in Acanthodactylus beershebensis lizards results from the changing optical properties of single types of developing chromatophore cells. The blue tail colors of hatchlings are produced by incoherent scattering from premature guanine crystals in underdeveloped iridophore cells. Cryptic tail colors emerge during chromatophore maturation upon reorganization of the guanine crystals into a multilayer reflector concomitantly with pigment deposition in the xanthophores. Ontogenetic changes in adaptive colors can thus arise not via the exchange of different optical systems, but by harnessing the timing of natural chromatophore development. The incoherent scattering blue color here differs from the multilayer interference mechanism used in other blue-tailed lizards, indicating that a similar trait can be generated in at least two ways. This supports a phylogenetic analysis showing that conspicuous tail colors are prevalent in lizards and that they evolved convergently. Our results provide an explanation for why certain lizards lose their defensive colors during ontogeny and yield a hypothesis for the evolution of transiently functional adaptive colors. [ABSTRACT FROM AUTHOR]

Formation of a p-n junction-like with a large built-in field is demonstrated at the nanoscale, using two types of semiconducting nanoparticles, CsPbBr3 nanocrystals and CdSe nanoplatelets, capped with molecular linkers. By exploiting chemical recognition of the capping molecules, the two types of nanoparticles are brought into mutual contact, thus initiating spontaneous charge transfer and the formation of a strong junction field. Depending on the choice of capping molecules, the magnitude of the latter field is shown to vary in a broad range, corresponding to an interface potential step as large as ∼1 eV. The band diagram of the system as well as the emergence of photoinduced charge transfer processes across the interface is studied here by means of optical and photoelectron based spectroscopies. Our results propose an interesting template for generating and harnessing internal built-in fields in heterogeneous nanocrystal solids. [ABSTRACT FROM AUTHOR]

Formation of highly interpenetrated frameworks is demonstrated. An interesting observation is the presence of very large adamantane‐shaped cages in a single network, making these crystals new entries in the collection of diamondoid‐type metal–organic frameworks (MOFs). The frameworks were constructed by assembling tetrahedral pyridine ligands and copper dichloride. Currently, the networks' degree of interpenetration is among the highest reported and increases when the size of the ligand is increased. Highly interpenetrated frameworks typically have low surface contact areas. In contrast, in our systems, the voids take up to 63 % of the unit cell volume. The MOFs have chiral features but are formed from achiral components. The chirality is manifested by the coordination chemistry around the metal center, the structure of the helicoidal channels, and the motifs of the individual networks. Channels of both handednesses are present within the unit cells. This phenomenon shapes the walls of the channels, which are composed of 10, 16, or 32 chains correlated with the degree of interpenetration 10‐, 16‐, and 32‐fold, respectively. By changing the distance between the center of the ligand and the coordination moieties, we succeeded in tuning the diameter of the channels. Relatively large channels were formed, having diameters up to 31.0 Å×14.8 Å. [ABSTRACT FROM AUTHOR]

Reflective assemblies of high refractive index organic crystals are used to produce striking optical phenomena in organisms based on light reflection and scattering. In aquatic animals, organic crystal-based reflectors are used both for image-formation and to increase photon capture. Here we report the characterization of a poorly-documented reflector in the eye of the shrimp L. vannamei lying 150 μm below the retina, which we term the proximal reflective layer (PR-layer). The PR-layer is made from a dense but disordered array of polycrystalline isoxanthopterin nanoparticles, similar to those recently reported in the tapetum of the same animal. Each spherical nanoparticle is composed of numerous isoxanthopterin single crystal plates arranged in concentric lamellae around an aqueous core. The highly reflective plate faces of the crystals are all aligned tangentially to the particle surface with the optical axes projecting radially outwards, forming a birefringent spherulite which efficiently scatters light. The nanoparticle assemblies form a broadband reflective sheath around the screening pigments of the eye, resulting in pronounced eye-shine when the animal is viewed from a dorsal-posterior direction, rendering the eye pigments inconspicuous. We assess possible functions of the PR-layer and conclude that it likely functions as a camouflage device to conceal the dark eye pigments in an otherwise largely transparent animal. [ABSTRACT FROM AUTHOR]

Knopp et al. [J. Raman Spectrosc. 31, 51 (2000)] have recently used resonant femtosecond coherent anti-Stokes Raman spectroscopy (CARS) to prepare and probe highly excited vibrational wave packets on the ground electronic potential surface of molecular iodine. The experiment uses a sequence of three resonant femtosecond pulses with two independently variable time delays. The first two pulses act as a pump and dump sequence to create a predefined, highly excited wave packet on the ground electronic state, whose amplitude is optimized by selecting the proper pump–dump (Raman) frequency difference and varying the time delay. The third pulse promotes the pump–dump wave packet to an excited electronic state, resulting in subsequent coherent emission of light at the anti-Stokes frequency. This fully-resonant CARS signal, measured as a function of time delay between the second and third pulses, oscillates at a frequency characteristic of the pump–dump wave packet. Due to anharmonicity, this frequency is a sensitive measure of the amount of vibrational excitation. Knopp et al. observed that under certain conditions the signal exhibits pronounced beating between the pump–dump wave packet frequency and the frequency characteristic of the bottom of the ground state well. In this paper we show that these beats arise only when the final pump–dump–pump wave packet is above the excited state dissociation threshold of the molecule. We derive analytical expressions showing that under these conditions, where the polarization is short-lived, there may be strong interferences between the contributions from molecules originally in different vibrational states of the thermal ensemble. In contrast, the CARS polarization in the below threshold case is long-lived, and these interferences cancel. Numerical evaluation of the CARS signal through vibrational wave packet propagation confirms the predictions of the analytical theory and reproduc... [ABSTRACT FROM AUTHOR]

The characterization of the robust and adaptive self-assembled supramolecular three-dimensional network system via cryo-TEM, cryo-SEM, and rheological measurements is described. The dual sensibility toward chemical reduction and temperature with a distinct and interrelated response to each of the applied stimuli and the strong adsorption of visible light and good exciton mobility exhibited by the system could find potential applications in the area of adaptive functional materials.