Spectral dynamics of shift current in ferroelectric semiconductor SbSI.

Photoexcitation in solids brings about transitions of electrons/holes between different electronic bands. If the solid lacks an inversion symmetry, these electronic transitions support spontaneous photocurrent due to the geometric phase of the constituting electronic bands: the Berry connection. This photocurrent, termed shift current, is expected to emerge on the timescale of primary photoexcitation process. We observe ultrafast evolution of the shift current in a prototypical ferroelectric semiconductor antimony sulfur iodide (SbSI) by detecting emitted terahertz electromagnetic waves. By sweeping the excitation photon energy across the bandgap, ultrafast electron dynamics as a source of terahertz emission abruptly changes its nature, reflecting a contribution of Berry connection on interband optical transition. The shift excitation carries a net charge flow and is followed by a swing over of the electron cloud on a subpicosecond timescale. Understanding these substantive characters of the shift current with the help of first-principles calculation will pave the way for its application to ultrafast sensors and solar cells.

Downward Terrestrial Gamma-Ray Flash Observed in a Winter Thunderstorm.

During a winter thunderstorm on 24 November 2017, a strong burst of gamma rays with energies up to ∼10 MeV was detected coincident with a lightning discharge, by scintillation detectors installed at the Kashiwazaki-Kariwa Nuclear Power Station at sea level in Japan. The burst had a subsecond duration, which is suggestive of photoneutron production. The leading part of the burst was resolved into four intense gamma-ray bunches, each coincident with a low-frequency radio pulse. These bunches were separated by 0.7-1.5 ms, with a duration of ≪1 ms each. Thus, the present burst may be considered as a "downward" terrestrial gamma-ray flash (TGF), which is analogous to upgoing TGFs observed from space. Although the scintillation detectors were heavily saturated by these bunches, the total dose associated with them was successfully measured by ionization chambers, employed by nine monitoring posts surrounding the power plant. From this information and Monte Carlo simulations, the present downward TGF is suggested to have taken place at an altitude of 2500±500 m, involving 8_{-4}^{+8}×10^{18} avalanche electrons with energies above 1 MeV. This number is comparable to those in upgoing TGFs.

Mott transition by an impulsive dielectric breakdown.

The transition of a Mott insulator to metal, the Mott transition, can occur via carrier doping by elemental substitution, and by photoirradiation, as observed in transition-metal compounds and in organic materials. Here, we show that the application of a strong electric field can induce a Mott transition by a new pathway, namely through impulsive dielectric breakdown. Irradiation of a terahertz electric-field pulse on an ET-based compound, κ-(ET) 2Cu[N(CN) 2]Br (ET:bis(ethylenedithio)tetrathiafulvalene), collapses the original Mott gap of ∼30 meV with a ∼0.1 ps time constant after doublon-holon pair productions by quantum tunnelling processes, as indicated by the nonlinear increase of Drude-like low-energy spectral weights. Additionally, we demonstrate metallization using this method is faster than that by a femtosecond laser-pulse irradiation and that the transition dynamics are more electronic and coherent. Thus, strong terahertz-pulse irradiation is an effective approach to achieve a purely electronic Mott transition, enhancing the understanding of its quantum nature.

Oxygen ultra-fine bubbles water administration prevents bone loss of glucocorticoid-induced osteoporosis in mice by suppressing osteoclast differentiation.

Oxygen ultra-fine bubbles (OUB) saline injection prevents bone loss of glucocorti\coid-induced osteoporosis in mice, and OUB inhibit osteoclastogenesis via RANK-TRAF6-c-Fos-NFATc1 signaling and RANK-p38 MAPK signaling in vitro. INTRODUCTION: Ultra-fine bubbles (<200 nm in diameter) have several unique properties, and they are tested in various medical fields. The purpose of this study was to investigate the effects of oxygen ultra-fine bubbles (OUB) on glucocorticoid-induced osteoporosis (GIO) model mice. METHODS: Prednisolone (PSL, 5 mg) was subcutaneously inserted in 6-month-old male C57BL/6J mice, and 200 µl of saline, OUB-diluted saline, or nitrogen ultra-fine bubbles (NUB)-diluted saline was intraperitoneally injected three times per week for 8 weeks the day after operations. Mice were divided into four groups; (1) control, sham-operation + saline; (2) GIO, PSL + saline; (3) GIO + OUB, PSL + OUB saline; (4) GIO + NUB, PSL + NUB saline. The effects of OUB on osteoblasts and osteoclasts were examined by serially diluted OUB medium in vitro. RESULTS: Bone mass was significantly decreased in GIO [bone volume/total volume (%): control vs. GIO 12.6 vs. 7.9; p < 0.01] while significantly preserved in GIO + OUB (GIO vs. GIO + OUB 7.9 vs. 12.9; p < 0.05). In addition, tartrate-resistant acid phosphatase (TRAP)-positive cells in the distal femur [mean osteoclasts number/bone surface (mm-1)] was significantly increased in GIO (control vs. GIO 6.8 vs. 11.6; p < 0.01) while suppressed in GIO + OUB (GIO vs. GIO + OUB 11.6 vs. 7.5; p < 0.01). NUB did not affect these parameters. In vitro experiments revealed that OUB significantly inhibited osteoclastogenesis by inhibiting RANK-TRAF6-c-Fos-NFATc1 signaling, RANK-p38 MAPK signaling, and TRAP/Cathepsin K/DC-STAMP mRNA expression in a concentration-dependent manner. OUB did not affect osteoblastogenesis in vitro. CONCLUSIONS: OUB prevent bone loss in GIO mice by inhibiting osteoclastogenesis.

Terahertz-Field-Induced Large Macroscopic Polarization and Domain-Wall Dynamics in an Organic Molecular Dielectric.

A rapid polarization control in paraelectric materials is important for an ultrafast optical switching useful in the future optical communication. In this study, we applied terahertz-pump second-harmonic-generation-probe and optical-reflectivity-probe spectroscopies to the paraelectric neutral phase of an organic molecular dielectric, tetrathiafulvalene-p-chloranil and revealed that a terahertz pulse with the electric-field amplitude of ∼400 kV/cm produces in the subpicosecond time scale a large macroscopic polarization whose magnitude reaches ∼20% of that in the ferroelectric ionic phase. Such a large polarization generation is attributed to the intermolecular charge transfers and breathing motions of domain walls between microscopic neutral and ionic domains induced by the terahertz electric field.

Time-Reversal Measurement of the p-Wave Cross Sections of the

The cross sections of the ^{7}Be(n,α)^{4}He reaction for p-wave neutrons were experimentally determined at E_{c.m.}=0.20-0.81 MeV slightly above the big bang nucleosynthesis (BBN) energy window for the first time on the basis of the detailed balance principle by measuring the time-reverse reaction. The obtained cross sections are much larger than the cross sections for s-wave neutrons inferred from the recent measurement at the n_TOF facility in CERN, but significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the ^{7}Be(n,α)^{4}He reaction rate is not large enough to solve the cosmological lithium problem, and this conclusion agrees with the recent result from the direct measurement of the s-wave cross sections using a low-energy neutron beam and the evaluated nuclear data library ENDF/B-VII.1.

Terahertz Dynamics of a Topologically Protected State: Quantum Hall Effect Plateaus near the Cyclotron Resonance of a Two-Dimensional Electron Gas.

We measure the Hall conductivity of a two-dimensional electron gas formed at a GaAs/AlGaAs heterojunction in the terahertz regime close to the cyclotron resonance frequency using highly sensitive Faraday rotation measurements. The sample is electrically gated, allowing the electron density to be changed continuously by more than a factor of 3. We observe clear plateaulike and steplike features in the Faraday rotation angle vs electron density and magnetic field (Landau-level filling factor) even at fields or frequencies very close to cyclotron resonance absorption. These features are the high frequency manifestation of quantum Hall plateaus-a signature of topologically protected edge states. We observe both odd and even filling factor plateaus and explore the temperature dependence of these plateaus. Although dynamical scaling theory begins to break down in the frequency region of our measurements, we find good agreement with theory.

Randomized trial of preoperative docetaxel with or without capecitabine after 4 cycles of 5-fluorouracil­ epirubicin­cyclophosphamide (FEC) in early-stage breast cancer: exploratory analyses identify Ki67 as a predictive biomarker for response to neoadjuvant chemotherapy.

This randomized, multicenter study compared the efficacy of docetaxel with or without capecitabine following fluorouracil/epirubicin/cyclophosphamide (FEC) therapy in operable breast cancer and investigated the role of Ki67 as a predictive biomarker. Patients were randomized to 4 cycles of docetaxel/capecitabine (docetaxel: 75 mg/m2 on day 1; capecitabine: 1,650 mg/m2 on days 1­14 every 3 weeks) or docetaxel alone (75 mg/m2 on day 1 every 3 weeks) after completion of 4 cycles of FEC (5-fluorouracil 500 mg/m2, epirubicin 100 mg/m2 and cyclophosphamide 500 mg/m2 on day 1 every 3 weeks). The primary endpoint was the pathological complete response (pCR) rate. Predictive factor analysis was conducted using clinicopathological markers, including hormone receptors and Ki67 labeling index (Ki67LI). A total of 477 patients were randomized; the overall response in the docetaxel/capecitabine and docetaxel groups was 88.3 and 87.4 %, respectively. There were no significant differences in the pCR rate (docetaxel/capecitabine: 23 %; docetaxel: 24 %; p = 0.748), disease-free survival, or overall survival. However, patients with mid-range Ki67LI (10­20 %) showed a trend towards improved pCR rate with docetaxel/capecitabine compared to docetaxel alone. Furthermore, multivariate logistic regression analysis showed pre-treatment Ki67LI (odds ratio 1.031; 95 % CI 1.014­1.048; p = 0.0004) to be a significant predictor of pCR in this neoadjuvant treatment setting. Docetaxel/capecitabine (after 4 cycles of FEC) did not generate significant improvement in pCR compared to docetaxel alone. However, exploratory analyses suggested that assessment of pre-treatment Ki67LI may be a useful tool in the identification of responders to preoperative docetaxel/capecitabine in early-stage breast cancer.

Optical imaging of retina in response to grating stimuli in cats.

We examined the intrinsic signals in response to grating stimuli in order to determine whether the light-evoked intrinsic signals of the retina are due to changes in the photoreceptor activities induced by the image projected on to the retina or are due to neural activities of the inner retina. The retinas of the left eye of 12 cats under general anesthesia were examined by a functional imaging fundus camera. Near infrared light was used to monitor the reflectance changes (RCs) of the retina. Vertical grating were used to stimulate the retina at 4 Hz. The spatial frequencies of the gratings were 0.05, 0.11, 0.22, 0.43, 0.86, 1.73, and 3.46 cycles/degree (cpd). Ten images were averaged and used to analyze the RCs to obtain the peak value (PV) of a two dimensional fast Fourier transfer of the RCs. The wavefront aberrations (WA) were measured with a compact wavefront aberrometer and the spatial modulation transfer function (MTF) of the eye was calculated. The retinal reflectance image had a grating pattern. The PV of the spatial sensitivity curve was highest at low spatial frequencies (0.05 and 0.11 cpd), and the sensitivity decreased steeply with an increase in the spatial frequency. RCs were not detectable at 3.46 cpd. The MTF decreased gradually with increases in the spatial frequencies and was 0.68 at 3.46 cpd. The reflectance pattern of the retinal intrinsic signal elicited by grating stimuli of different spatial frequencies was different from that of the MTF. This suggests that the intrinsic signal represents not only the response of the photoreceptors but also other neuronal or vascular changes in the retina.

Overt nephrogenic diabetes insipidus in mice lacking the CLC-K1 chloride channel.

CLC-K1 is a kidney-specific chloride channel that mediates transepithelial chloride transport in the thin ascending limb of Henle's loop (tAL) in the inner medulla. Transport of NaCl in the tAL is thought to be a component of urinary concentration in a passive model of the countercurrent multiplication system, but there has been no direct evidence that CLC-K1 is involved in urine concentration. To analyse the physiological function of CLC-K1 in vivo, we generated mice lacking CLC-K1 by targeted gene disruption. Clcnk1-/- mice were physically normal appearance, but produced approximately five times more urine than Clcnk1+/- and Clcnk1+/+ mice. After 24 hours of water deprivation, Clcnk1-/- mice were severely dehydrated and lethargic, with a decrease of approximately 27% in body weight. Intraperitoneal injection of the V2 agonist 1-deamino-8-D-arginine vasopressin (dDAVP) induced a threefold increase in urine osmolarity in Clcnk1+/- and Clcnk1+/+ mice, whereas only a minimal increase was seen in Clcnk1-/- mice, indicating nephrogenic diabetes insipidus. After in vitro perfusion of the tAL, the lumen-to-bath chloride gradient did not produce a diffusion potential in Clcnk1-/- mice in contrast to Clcnk1+/+ and Clcnk1+/- mice. These results establish that CLC-K1 has a role in urine concentration, and that the countercurrent system in the inner medulla is involved in the generation and maintenance of hypertonic medullary interstitium.

Masseter EMG activity during sleep and sleep bruxism.

The masseter muscle is involved in the complex and coordinated oromotor behaviors such as mastication during wakefulness. The masseter electromyographic (EMG) activity decreases but does not disappear completely during sleep: the EMG activity is generally of low level and inhomogeneous for the duration, amplitude and intervals. The decreased excitability of the masseter motoneurons can be determined by neural substrates for NREM and REM sleep. The masseter EMG activity is increased in association with the level of arousal fluctuations within either sleep state. In addition, there are some motor events such as REM twitches, swallowing and rhythmic masticatory muscle activity (RMMA), whose generation might involve the additional activation of specific neural circuits. Sleep bruxism (SB) is characterized by exaggerated occurrence of RMMA. In SB, the rhythmic activation of the masseter muscle can reflect the rhythmic motor inputs to motoneurons through, at least in part, common neural circuits for generating masticatory rhythm under the facilitatory influences of transient arousals. However, it remains elusive as to which neural circuits determine the genesis of sleep bruxism. Based on the available knowledge on the masseter EMG activity during sleep, this review presents that the variety of the masseter EMG phenotypes during sleep can result from the combinations of the quantitative, spatial and temporal neural factors eventually sending net facilitatory inputs to trigeminal motoneurons under sleep regulatory systems.

Do Outcomes between Women and Men Differ after Endovascular Thrombectomy? A Meta-analysis.

BACKGROUND: Research on the presence of sex-based differences in the outcomes of patients undergoing endovascular thrombectomy for acute ischemic stroke has reached differing conclusions. PURPOSE: This review aimed to determine whether sex influences the outcome of patients with large-vessel occlusion stroke undergoing endovascular thrombectomy. STUDY SELECTION: We performed a systematic review and meta-analysis of endovascular thrombectomy studies with either stratified cohort outcomes according to sex (females versus males) or effect size reported for the consequence of sex versus outcomes. We included 33 articles with 7335 patients. DATA ANALYSIS: We pooled ORs for the 90-day mRS score, 90-day mortality, symptomatic intracranial hemorrhage, and recanalization. DATA SYNTHESIS: Pooled 90-day good outcomes (mRS ≤ 2) were better for men than women (OR = 1.29; 95% CI, 1.09-1.53; P = <.001, I2 = 56.95%). The odds of the other outcomes, recanalization (OR = 0.94; 95% CI, 0.77-1.15; P = .38, I2 = 0%), 90-day mortality (OR = 1.11; 95% CI, 0.89-1.38; P = .093, I2 = 0%), and symptomatic intracranial hemorrhage (OR = 1.40; 95% CI, 0.99-1.99; P = .069, I2 = 0%) were comparable between men and women. LIMITATIONS: Moderate heterogeneity was found. Most studies included were retrospective in nature. In addition, the randomized trials included were not specifically designed to compare outcomes between sexes. CONCLUSIONS: Women undergoing endovascular thrombectomy for large-vessel occlusion have inferior 90-day clinical outcomes. Sex-specific outcomes should be investigated further in future trials as well as pathophysiologic studies.

Terahertz-field-induced polar charge order in electronic-type dielectrics.

Ultrafast electronic-phase change in solids by light, called photoinduced phase transition, is a central issue in the field of non-equilibrium quantum physics, which has been developed very recently. In most of those phenomena, charge or spin orders in an original phase are melted by photocarrier generations, while an ordered state is usually difficult to be created from a non-ordered state by a photoexcitation. Here, we demonstrate that a strong terahertz electric-field pulse changes a Mott insulator of an organic molecular compound in κ-(ET)2Cu[N(CN)2]Cl (ET = bis(ethylenedithio)tetrathiafulvalene), to a macroscopically polarized charge-order state; herein, electronic ferroelectricity is induced by the collective intermolecular charge transfers in each dimer. In contrast, in an isostructural compound, κ-(ET)2Cu2(CN)3, which shows the spin-liquid state at low temperatures, a similar polar charge order is not stabilized by the same terahertz pulse. From the comparative studies of terahertz-field-induced second-harmonic-generation and reflectivity changes in the two compounds, we suggest the possibility that a coupling of charge and spin degrees of freedom would play important roles in the stabilization of polar charge order.

Optical Hall effect in the integer quantum Hall regime.

Optical Hall conductivity σ{xy}(ω) is measured from the Faraday rotation for a GaAs/AlGaAs heterojunction quantum Hall system in the terahertz-frequency regime. The Faraday rotation angle (∼ fine-structure constant ∼ mrad) is found to significantly deviate from the Drude-like behavior to exhibit a plateaulike structure around the Landau-level filling ν=2. The result, which fits with the behavior expected from the carrier localization effect in the ac regime, indicates that the plateau structure, although not quantized, still exists in the terahertz regime.

Detection of umbilical venous constriction by Doppler flow measurement at midgestation.

OBJECTIVES: To investigate whether umbilical venous velocity and venous velocity pulsation are associated with umbilical vein diameter, umbilical ring diameter and umbilical cord coiling index at midgestation. METHODS: Two hundred and eighty pregnant women were enrolled in the study at between 18 and 24 weeks of gestation. The diameter of the umbilical cord and internal diameter of the umbilical vein in a free loop and at the ring, and the umbilical coiling index, were measured using ultrasonography. Umbilical venous velocities were measured by Doppler ultrasonography at the umbilical ring and a free loop of the cord. RESULTS: All variables were successfully measured in 92% of the patients. There were negative correlations between the diameters of the umbilical ring and of the umbilical vein at the ring and the venous velocity at the umbilical ring. The venous velocity at the umbilical ring was significantly higher and the umbilical ring diameter was significantly lower in fetuses with umbilical venous pulsation at the free loop. Significant correlations were observed between the venous velocity and amplitude of pulsation. Venous pulsations at the free loop were frequently observed in fetuses with a hypercoiled cord. CONCLUSION: High venous velocity and increased venous pulsation at the umbilical ring may be associated with umbilical cord constriction.

Study of charged particle activation analysis (II): Determination of boron concentration in human blood samples.

Boron Neutron Capture Therapy (BNCT) is a radiotherapy for the treatment of intractable cancer. In BNCT precise determination of 10B concentration in whole blood sample before neutron irradiation of the patient, as well as accurate neutron dosimetry, is crucial for control of the neutron irradiation time. For this purpose ICP-AES and neutron induced prompt γ-ray analysis are generally used. In Ibaraki Neutron Medical Research Center (iNMRC), an intense proton beam will be accelerated up to 8 MeV, which can also be used for Charged Particle Activation Analysis (CPAA). Thus, in this study, we apply the CPAA utilizing the proton beam to non-destructive and accurate determination of 10B concentration in whole blood sample. A CPAA experiment is performed by utilizing an 8 MeV proton beam from the tandem accelerator of Nuclear Science Research Institute in Japan Atomic Energy Agency. The 478 keV γ-ray of 7Be produced by the 10B(p, α)7Be reaction is used to quantify the 10B in human blood. The 478 keV γ-ray intensity is normalized by the intensities of the 847 keV and 1238 keV γ-rays of 56Co originating from Fe in blood. The normalization methods were found to be linear in the range of 3.27 µg 10B/g to 322 µg 10B/g with correlation coefficients of better than 0.9999.

Studies on the posterior silk gland of the silkworm, Bombyx mori. I. Growth of posterior silk gland cells and biosynthesis of fibroin during the fifth larval instar.

Growth of the posterior silk gland and biosynthesis of fibroin during the fifth larval instar of the silkworm, Bombyx mori, have been studied. In accordance with the exponential increase in the wet weight of the gland, the amounts of DNA, RNA, protein, and lipids per animal increased rapidly in the early stage of the fifth instar (0-96 hr). Biosynthesis of fibroin, on the contrary, mainly proceeds in the later stage of the fifth instar (120-192 hr). Electron microscopical observations have shown that, in the very early stage (0-12 hr), a number of free ribosomes exist in the cytoplasm. Rough endoplasmic reticulum (ER) with closely spaced cisternae was also observed. Then rough ER starts to proliferate rapidly, and at the same time lamellar ER is rapidly or gradually transformed into vesicular or tubular forms. In the later stage of the fifth instar (120-192 hr), the cytoplasm is mostly filled with tubular or vesicular ER. Golgi vacuoles, free vacuoles (fibroin globules), and mitochondria are also observed. It is concluded that in the early stage of the fifth instar the cellular structures necessary for the biosynthesis of fibroin are rapidly formed, while in the later stage the biosynthesis of fibroin proceeds at a maximum rate and utilizes these structures.

Studies on the posterior silk gland of the silkworm, Bombyx mori. II. Cytolytic processes in posterior silk gland cells during metamorphosis from larva to pupa.

Cytolytic processes in posterior silk gland cells of the silkworm, Bombyx mori, during metamorphosis from larva to pupa have been studied. During this stage, the wet weight and the amounts of RNA and protein of the gland decrease rapidly and markedly, while the amount of DNA decreases slowly and slightly. The ultrastructural changes observed at the beginning of the prepupal stage consist of the appearance or the increase in the number of autophagosomes containing endoplasmic reticulum (ER), or "early autophagosomes" as we have called them, which seem to be gradually transformed to autolysosomes. A number of usual lysosomes, which frequently contain myelin figures, also appear in the cytoplasm. Sometimes they fuse with each other to form large conglomerates. In the middle of the prepupal stage, a number of smooth membrane-bounded vacuoles appear in cytoplasm. Towards the end of the prepupal stage the partition or sequestration of cytoplasm was observed. Thus large autophagosomes containing cytoplasmic organelles such as rough ER and/or mitochondria are formed. The nucleus is partitioned in a similar way by smooth membranes, and then autophagosomes containing condensed chromatin blocks are formed. These various kinds of autophagosomes, or "late autophagosomes" as we have generally called them, are continuously released into the hemolymph until the gland is completely disintegrated.

Studies on the posterior silk gland of the silkworm, Bombyx mori. 3. Ultrastructural changes of posterior silk gland cells in the fourth larval instar.

The development of the cells in the posterior silk gland of the silkworm, Bombyx mori, during the fourth larval instar has been studied. In the early stages of this instar, the wet weight of the gland and the amounts of RNA, DNA, and protein per animal increase logarithmically until they reach a stationary state at about 72 hr. At around 96 hr of the fourth instar, the larvae enter the molting state, which lasts for about 24 hr until the fourth ecdysis. Towards the end of the molt stage, the growth of the silk gland is resumed. Electron microscopical observation shows that in the early intermolt stage the cytoplasm is filled with free ribosomes and with rough endoplasmic reticulum (ER), first of the lamellar type (0-6 hr) and then of the vesicular or tubular type. The Golgi apparatus also is well developed. At the beginning of the molt stage (90-96 hr), however, most of the ER becomes lamellar in type, concentric lamellar structures being occasionally observed, and the Golgi vacuoles disappear. Autophagosomes and lysosomes increase markedly and the apical portion of the cytoplasm becomes extensively vacuolated; this suggests that the secretory activities are completely depressed, and pronounced degenerative changes appear during the molt stage. Towards the end of the molt stage, large lamellar ER elements are fragmented into smaller lamellae and there is a pronounced increase in the number of free ribosomes.

Ribosome crystallization in chicken embryos. II. Conditions for the formation of ribosome tetramers in vitro.

Slow cooling of fertilized chicken eggs permits the elongation and termination of nascen(t) polypeptides in the polysomes but prevents the initiation of new protein chains. This leads to polysome disaggregation during the first 30 min of cooling, and to the formation, of a pool of inactive ribosomes prone to crystallization. After 2 hr these ribosomes began to form tetramers, which do not contain any labeled proteins synthesized during cooling. If protein synthesis is inhibited by cycloheximide, added to eggs before cooling, tetramer formation in the embryos is prevented. Puromycin, on the other hand, leads to polysome disassembly and does not prevent tetramer formation. Rapid cooling of explanted embryos after short incubation at 37 degrees C, with or without cycloheximide, largely prevents polysome disaggregation and the formation of tetramers. On the other hand, the addition of puromycin to explanted embryos promotes tetramer formation after rapid cooling. When cooled eggs are rewarmed, tetramers are disassembled into monomers, even if protein synthesis is inhibited. When those embryos were rapidly recooled tetramers reformed spontaneously from tetramer-derived monomers, even in the presence of cycloheximide. We conclude that the formation of tetramers at low temperature is an inherent property of the normal ribosomes.