The phase relations of calcium fluoride (fluorite) to 60 kbars and 1800°C

We present here a somewhat tentative phase diagram for calcium fluoride (fluorite). We find three stable phases as well as a field of liquid. We show here the slope of the melting curve, the β-γ phase boundary, the α-β phase boundary and the approximate α-γ phase boundary. Our extrapolated α-γ phase boundary required considerable curvature in order for it to coincide with the reported 1 atmosphere Dandekar and Jamieson value of the transition.     

Temperature dependence of bismuth structures under high pressure

It is unclear whether there is a liquid-liquid phase transition or not in the bismuth melt at high temperature and high pressure. If so, it will be necessary to confirm the boundary of the liquid-liquid phase transition and clarify whether it is a first-order phase transition. Here, based on x-ray absorption spectra and simulations, the temperature dependence of bismuth structures is investigated under different pressures. According to the similarity of characteristic peaks of x-ray absorption near edge structure (XANES) spectra, we estimate the possible temperature ranges of liquid-liquid phase transition to be 779-799 K at 2.74 GPa and 859-879 K at 2.78 GPa, 809-819 K at 3.38 GPa and 829-839 K at 3.39 GPa and 729-739 K at 4.78 GPa. Using ab initio molecular dynamics (AIMD) simulations, we obtain the stable structures of the bismuth melt at different temperatures and pressures, and calculated their electronic structures. Meanwhile, two stable phases (phase III-like and phase IV-like) of bismuth melts are obtained from different initial phases of bismuth solids (phase III and phase IV) under the same condition (3.20 GPa and 800 K). Assuming that the bismuth melt undergoes a phase transition from IV-like to III-like between 809 K and 819 K at 3.38 GPa, the calculated electronic structures are consistent with the XANES spectra, which provides a possible explanation for the first-order liquid-liquid phase transition.     

Induced Smectic-G Phase through Intermolecular Hydrogen Bonding. Part VI: Thermal and phase Behavior of 2-(4-Decyloxybenzylidene Imino)-5-Chloropyridine (Dacp : Aba) Complexes

A novel series of liquid-crystalline complexes involving intermolecular hydrogen bonding between p - n -alkoxybenzoic acids (ABA) (where alkoxy = propoxy- to decyloxy- and dodecyloxy-) and 2-(4-decyloxybenzylidene imino)-5-chloropyridine (DACP) have been synthesized and their thermal and phase behaviour are studied by Thermal Microscopy (TM) and Differential Scanning Calorimetry (DSC). A detailed IR spectral investigation in solid and solution states confirms the formation of H-bonding between pyridine ring nitrogen and -COOH group of DACP and ABA respectively. Comparative thermal analyses of both free p - n -alkoxybenzoic acids and H-bonded complexes suggest the inducement of smectic-G phase in all the complexes, with a simultaneous quenching of smectic-C phase. The comparative thermal and phase behaviour with analogous series 2-(4-nonyloxybenzylidene imino)-5-chloropyridine : p - n -alkoxybenzoic acids (NACP : ABA) and 2-amino-5-chloropyridine : p - n -alkoxybenzoic acids (ACP : ABA) also imply the stabilization of the induced phase with a wide thermal span.     

Unusual sequence of commensurate-incommensurate phase transitions observed in KLiSO4

An unusual structural phase transition sequence is observed in KLiSO₄ by EPR: high temperature prototype phase -incommensurately modulated phase - commensurately modulated phase - incommensurately modulated phase - low temperature prototype phase (reentrant phase). The low temperature phase has the same symmetry C⁶₆ of the high temperature prototype phase. The main feature of the modulation are rotations of the sulphate tetrahedra, which were precisely determined in the commensurately modulated phase.     

Multi-wave trains and Sasa - Satsuma freak events generation in an optical metamaterial

In this work, we present a new Ansatz function called ”type I Ansatz function” with seven collective coordinates compared to the conventional Gaussian Ansatz function with six collective coordinates. We show that the additional coordinate called ”nonlinear phase” will allow us to improve the technique of measurement of internal excitation leading to the generation of rogue events. Moreover, the nonlinear phase coordinate will give supplemental details on the phase distortions during the generation of specific rogue events such as wall of waves, tree structures, double Kuznetsov - Ma breathers and Sasa - Satsuma rogue waves. The propagation will be modeled by a higher - order nonlinear Schrödinger equation when second - and third - order dispersions, self - and quintic - phase modulations and self - steepening come into play for negative index and absorption regimes. The conditions of stability of the soliton light pulse will also been investigated. The validity of our results is confirmed numerically by using a systematic computational approach.     

Quantitative differential phase measurement and imaging in transparent and turbid media by optical coherence tomography

Differential phase-contrast optical coherence tomography allows one to measure the path-length differences of two transversally separated beams in the nanometer range. We calculate these path-length differences from the phase functions of the interferometric signals. Pure phase objects consisting of chromium layers containing steps of approximately 100-200-nm height were imaged. Phase differences can be measured with a precision of +/-2 degrees , corresponding to a path-difference resolution of 2-3 nm. To investigate the influence of scattering, we imaged the phase objects through scattering layers with increasing scattering coefficients. The limit of phase imaging through these layers was at approximately 8-9 mean free path lengths thick (single pass).     

Medial efferent effects on auditory-nerve responses to tail-frequency tones II: alteration of phase

It is often assumed that at frequencies in the tuning-curve tail there is a passive, constant coupling of basilar-membrane motion to inner hair cell (IHC) stereocilia. This paper shows changes in the phase of auditory-nerve-fiber (ANF) responses to tail-frequency tones and calls into question whether basilar-membrane-to-IHC coupling is constant. In cat ANFs with characteristic frequencies > or = 10 kHz, efferent effects on the phase of ANF responses to tail-frequency tones were measured. Efferent stimulation caused substantial changes in ANF phase (deltaphi) (range -80 degrees to +60 degrees, average -15 degrees, a phase lag) with the largest changes at sound levels near threshold and 3-4 octaves below characteristic frequency (CF). At these tail frequencies, efferent stimulation had much less effect on the phase of the cochlear microphonic (CM) than on ANF phase. Thus, since CM is synchronous with basilar-membrane motion for low-frequency stimuli in the cochlear base, the efferent-induced change in ANF phase is unlikely to be due entirely to a change in basilar-membrane phase. At tail frequencies, ANF phase changed with sound level (often by 90 degrees-180 degrees) and the deltaphi from a fiber was positively correlated with the slope of its phase-versus-sound-level function at the same frequency, as if deltaphi were caused by a 2-4 dB increase in sound level. This correlation suggests that the processes that produce the change in ANF phase with sound level at tail frequencies are also involved in producing deltaphi. It is hypothesized that both efferent stimulation and increases in sound level produce similar phase changes because they both produce a similar mix of cochlear vibrational modes.     

AWG中波导间耦合造成的相位畸变的分析

用(1,1)阶Pad啨近似的广角BPM计算了阵列波导光栅(AWG)中由于阵列波导间耦合造成的相位畸变以及由于相位畸变引起的相位误差分别考虑了光从中心/非中心输入波导入射两种情况结果表明,波导间的耦合会造成显著的相位畸变,但由此引起的相位误差却很小,光从中心输入波导入射时对应的相位误差10-3rad,从非中心输入波导入射时的相位误差约为10-2rad针对波导阵列边缘效应引起的相位畸变,设计AWG结构时,在阵列部分两侧增加了边缘辅助波导结构,从而消除了边缘效应,使得边缘阵列波导对应的相位误差从10-1rad量级减小为10-3(10-2)rad量级.     

氨基酸DLH及其稀土镧配合物的高压红外和拉曼光谱研究

测定了DL-2-氨基-4-磺酸基-丁酸 [DLH, DL-Homocysteic acid, (NH+₃)-CH(COOH)-(CH₂)₂-SO-₃] 及其稀土La配合物[La(DLH)₂Cl₃·H₂O=LaL₂]在不同压力下的红外和拉曼光谱。DLH 在50 kbar左右压力以下存在两个压力诱导相转变区,它们分别在17和37 kbar左右,两者均为二级相转变,认为分子间氢键的存在是出现两个压力诱导相转变区的原因。在红外光谱中,SO-₃的对称伸缩振动的压力灵敏度(dν/dp)表现出与其他振动模式不同的变化趋势,它们在低压相区的平均压力灵敏度为0.30 cm-1·(kbar)-1、中压相区为0.32 cm-1·(kbar)-1、高压相区为0.41 cm-1·(kbar)-1,低压相区与高压相区的比值为0.72, 而其他振动模式刚好相反,低压相区与高压相区的比值为4.8。稀土La配合物LaL₂的生成,改变了分子间的氢键,在50 kbar左右压力以下只观察到1个压力诱导相转变区(27 kbar附近)。在红外光谱中,配合物LaL₂中SO-₃的反对称伸缩振动的压力灵敏度(dν/dp)也表现出与其他振动模式不同的变化趋势,它们在低压相区的平均压力灵敏度与高压相区的平均压力灵敏度的比值为0.43, 而其他振动模式的比值为2.5。     

New phase transition of solid bromine under high pressure

Solid bromine has been studied by x-ray absorption spectroscopy experiments up to a maximum pressure of 75 GPa. The data analysis of the extended fine structure reveals that the intramolecular distance first increases, reaching its maximum value at 25+/-5 GPa. From this value the intramolecular distance abruptly begins to decrease evidencing a nonpreviously observed phase transformation taking place at 25+/-5 GPa. A maximum variation of 0.08 A is observed at 65+/-5 GPa where again a phase transition occurs. This last transformation could correspond with the recently observed change to an incommensurate modulated phase. We discuss the possible generalization of the observed new phase transition at 25+/-5 GPa to the case of the other halogens.     

Wideband multichannel dispersion compensation based on a strongly chirped sampled Bragg grating and phase shifts

A novel multichannel dispersion compensator based on a strongly chirped sampled Bragg grating with phase shifts is demonstrated experimentally. With a single phase mask, various channel spacings and dispersion can be achieved by proper control of the sampling period and the phase shifts. A 100 GHz channel-spacing compensator with a dispersion of -1000 ps/nm and another 200 GHz channel-spacing compensator with a dispersion of -500 ps/nm are designed. As an example, a 40 channel, 100 GHz channel-spacing compensator with a dispersion of approximately -560 ps/nm is fabricated. All the designs are based on one phase mask, thus showing the flexibility of our method.     

Unstable growth of curvature perturbations in nonsingular bouncing cosmologies

Bouncing cosmologies require an ekpyrotic contracting phase (w?1) in order to achieve flatness, homogeneity, and isotropy. Models with a nonsingular bounce further require a bouncing phase that violates the null energy condition (w<-1). We show that the transition from the ekpyrotic phase to the bouncing phase creates problems for cosmological perturbations. A component of the adiabatic curvature perturbations, though decaying and negligible during the ekpyrotic phase, is exponentially amplified just before w approaches -1, enough to spoil the scale-invariant perturbation spectrum.     

单分子磁体-锰配合物的高压红外光谱研究

研究了单分子磁体锰配合物Ⅰ :[Mn1 2 O1 2 (O2 CC6 H4 3 Cl) 1 6 (H2 O) 3(3 Cl C6 H4 CO2 H) ]·(3 Cl C6 H4 CO2 H)和配合物Ⅱ :[Mn1 2 O1 2 (O2 CCH2 Br) 1 6 (H2 O) 4]·4 (CH2 Cl2 )的高压红外光谱 ,两者不同的压力诱导相转变的压力 (配合物Ⅰ :2 5～ 2 9kbar,配合物Ⅱ :2 9～ 35kbar)被观察到 ,两者均为二级压力诱导相转变。认为在压力诱导相转变时 ,也发生了配合物高自旋向低态自旋态的转变。配合物Ⅰ的平均压力灵敏度不同于通常情况 ,它在低压相区的平均压力灵敏度 (0 19cm- 1 ·kbar- 1 )比高压相区 (0 2 9cm- 1 ·kbar- 1 )低。而配合物Ⅱ与通常情况相似 ,在低压相区平均压力灵敏度 (0 34cm- 1 ·kbar- 1 )比高压相区 (0 2 3cm- 1 ·kbar- 1 )为高 ,即在高压相区的可压缩性比低压相区小。     

基于相位跳变区划分的相位展开方法

提出了一种相位跳变区域的确定方法，在此基础上提出一种基于相位跳变区划分的相位展开方法。计算机模拟和实验结果均证明：此方法对噪声有很强的抗干扰能力，能有效地实现带噪声的主值相位图的相位展开。     

Subfemtosecond synchronization of microwave oscillators with mode-locked Er-fiber lasers

We synchronize an 8.06 GHz microwave signal from a voltage-controlled oscillator with an optical pulse train from a 77.5 MHz mode-locked Er-fiber laser using a fiber-based optical-microwave phase detector. The residual phase noise between the optical pulse train and the synchronized microwave signal is -133 dBc/Hz (-154 dBc/Hz) at 1 Hz (5 kHz) offset frequency, which results in 838 as integrated rms timing jitter [1 Hz-1 MHz]. The long-term residual phase drift is 847 as (rms) measured over 2 h, which reaches 4×10(-19) fractional frequency instability at 1800 s averaging time. This method has a potential to provide both subfemtosecond-level short-term phase noise and long-term phase stability in microwave extraction from mode-locked fiber lasers.     

Breaking away: violation of distortion emission phase-frequency invariance at low frequencies

The phase versus frequency function of the distortion product otoacoustic emission (DPOAE) at 2f(1) - f(2) is approximately invariant at frequencies above 1.5 kHz in human subjects when recorded with a constant f(2)/f(1). However, a secular break from this invariance has been observed at lower frequencies where the phase-gradient becomes markedly steeper. Apical DPOAEs, such as 2f(1)?- f(2), are known to contain contributions from multiple sources. This experiment asked whether the phase behavior of the ear canal DPOAE at low frequencies is driven by the phase of the component from the distortion product (DP) region at 2f(1)?- f(2), which exhibits rapid phase accumulation. Placing a suppressor tone close in the frequency to 2f(1)?- f(2) reduced the contribution of this component to the ear canal DPOAE in normal-hearing adult human ears. When the contribution of this component was reduced, the phase behavior of the ear canal DPOAE was not altered, suggesting that the breaking from DPOAE phase invariance at low frequencies is an outcome of apical-basal differences in cochlear mechanics. The deviation from DPOAE phase invariance appears to be a manifestation of the breaking from approximate scaling symmetry in the human cochlear apex.     

A new structure of mercury under pressure

A reentrant trigonal (α)-Hg phase and a new hcp (δ)-Hg phase have been observed in energy dispersive X-ray diffraction measurements on mercury at room temperature and pressures up to 39 GPa. Studies at higher temperatures give first indications for a maximum in the α-β phase line at about 8(1) GPa and 380(10) K and an α-β-δ triple point at about 27(5) GPa and 180(20) K.     

Electronic correlations at the α-γ structural phase transition in paramagnetic iron

We compute the equilibrium crystal structure and phase stability of iron at the α(bcc)-γ(fcc) phase transition as a function of temperature, by employing a combination of ab initio methods for calculating electronic band structures and dynamical mean-field theory. The magnetic correlation energy is found to be an essential driving force behind the α-γ structural phase transition in paramagnetic iron.     

Investigations of pressure induced structural phase transformations in pentaerythritol

We have investigated the pressure induced structural changes in pentaerythritol {2,2-bis-(hydroxymethyl)-1,3-propanediol} with the help of X-ray diffraction studies. Our results show that this compound undergoes transformations to a lower symmetry phase between 5.2-5.9 GPa. It further undergoes phase transformations at ∼8.5 and ∼11 GPa; eventually evolving to a disordered phase beyond 14-15 GPa in agreement with our earlier Raman studies. On release of pressure from 18.5 GPa, the compound transforms back to the initial tetragonal phase.     

Phase polymorphism and electro-optical properties of a ferroelectric liquid crystal containing the biphenyl system

ABSTRACT

In this article we present results concerning phase transitions and physical properties of the ferroelectric phase of the compound (S)-4-(1-methylheptyloxy)biphenyl–4'-(heptyloxy phenyl)-4-carboxylate (MHOBOPO7). The compound has the following phases: smectic ferroelectric C (SmC*), chiral nematic N*, and two defected phases, TGB_C and blue phase. The mesomorphic properties were investigated by means of three complementary methods: differential scanning calorimetry, polarizing light optical microscopy, and transmitted light intensity. The electro-optical measurements were carried out on an ordered sample in a middle electric field during very slow cooling from the nematic phase to the ferroelectric phase.