The origin of the anomalous low-frequency vibrational behaviour of amorphous solids

1992 ◽  
Vol 02 ◽  
pp. C2-279-C2-283
Author(s):  
S. R. ELLIOTT
Keyword(s):  
Low Frequency ◽  
Peak Frequency ◽  
Amorphous Solids ◽  
Boson Peak ◽  
Low Frequencies ◽  
Crystalline Materials ◽  
Medium Range ◽  
Phonon Localization ◽  
Strong Scattering ◽  
Vibrational Density

The anomalous vibrational behaviour exhibited by non-crystalline materials - a peak in the vibrational density of states, and in the Raman spectrum (the boson peak) at low frequencies, and a peak in the heat capacity and a plateau in the thermal conductivity at low temperatures - is ascribed ta phonon localization associated with the strong scattering of phonons by density-fluctuation domains in the structure. Within such domains, short-range and medium-range arder is maintained, and outside them the material is structurally homogeneous and isotropie. This model can also explain the correlation between the boson-peak frequency and the position of the first sharp diffraction peak in the structure factor observed in a number of inorganie and polymerie amorphous solids.

scholarly journals Применение теории случайных матриц для описания бозонного пика в двумерных системах

2020 ◽  
Vol 62 (4) ◽  
pp. 603
Author(s):  
Д.А. Конюх ◽  
Я.М. Бельтюков
Keyword(s):  
Density Of States ◽  
Disordered Systems ◽  
Degrees Of Freedom ◽  
Matrix Theory ◽  
Three Dimensional ◽  
Amorphous Solids ◽  
Boson Peak ◽  
Two Dimensional ◽  
Reduced Density ◽  
Vibrational Density

The random matrix theory is applied to describe the vibrational properties of two-dimensional disordered systems with a large number of degrees of freedom. It is shown that the most significant mechanical properties of amorphous solids can be taken into account using the correlated Wishart ensemble. In this ensemble, an excess vibrational density of states over the Debye law is observed as a peak in the reduced density of states g(ω)/ω. Such a peak is known as the boson peak, which was observed in many experiments and numerical simulations for two-dimensional and three-dimensional disordered systems. It is shown that two-dimensional systems have a number of differences in the asymptotic behavior of the boson peak.

Low frequency vibrational density of state of highly permeable super glassy polynorbornenes – the Boson peak

2020 ◽  
Vol 22 (33) ◽  
pp. 18381-18387
Author(s):  
Reiner Zorn ◽  
Paulina Szymoniak ◽  
Mohamed A. Kolmangadi ◽  
Marcell Wolf ◽  
Dmitry A. Alentiev ◽  
...  
Keyword(s):  
Density Of States ◽  
Time Of Flight ◽  
Low Frequency ◽  
Boson Peak ◽  
Density Of State ◽  
Neutron Time ◽  
Incoherent Neutron ◽  
Vibrational Density

Inelastic incoherent neutron time-of-flight scattering was employed to measure the low frequency density of states for a series of addition polynorbornenes with bulky side groups.

Abstract 4666: Anatomic Substrate as Determinant of Dominant Frequency Dynamics During Human Ventricular Fibrillation

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Karthikeyan Umapathy ◽  
Stephane Masse ◽  
Elias Sevaptsidis ◽  
John Asta ◽  
Talha Farid ◽  
...  
Keyword(s):  
Low Frequency ◽  
Electrode Array ◽  
Peak Frequency ◽  
Dominant Frequency ◽  
Physiological Factors ◽  
Low Frequencies ◽  
Bipolar Electrodes ◽  
Df Analysis ◽  
Spatio Temporal ◽  
Spatial Locations

Background: Dominant frequency (DF) analysis is a common way of quantitatively studying the spatio-temporal variation of frequency during VF. Areas of high frequencies (e.g. rotors) and low frequencies (e.g. blocks) have been associated with the occurrence and maintenance of VF. However, the relation of these high or low frequency areas to anatomical or physiological substrate remains unclear. Objective: We tested the hypothesis that the Max-Min DF locations in the epicardium during VF are due to anatomical substrate. Methods and Results: We analyzed 33, 4 seconds VF episodes acquired from 6 isolated human hearts using a Langendorff setup. The hearts were received from the heart-transplanted patients with informed consent. Electrode array consisting 112 bipolar electrodes was used to acquire the surface unipolar and bipolar electrograms from the epicardium. DF was computed as the peak frequency of the VF segment from each of electrodes using Welch’s modified periodogram method. From the DF distribution, the regions of max and min frequencies were identified for LV and RV regions. Scar maps were computed for each of the 6 hearts using a previously published method by mapping the amplitude of bipolar electrograms (<0.5mv = scar) during the pacing protocol. The areas of max-min DF frequencies in each of the VF episode were compared to the corresponding spatial locations in the scar map. Table 1 shows the match between the max-min DF frequency locations and the scar locations. 50% of max-min DF frequencies locations match the scar locations and in 97% of the matched locations the max-min DF occur at the vicinity of the scar. Conclusion: During human VF, DF dynamics are only partially explained by the anatomical substrate. This suggests that ion channel heterogeneity and dynamic physiological factors may play an important role in determining fibrillation dynamics. Match Between Max-Min DF locations and Scar Locations

scholarly journals Low-frequency Raman scattering in binary silicate glass: Boson peak frequency and its general expression

2013 ◽  
Vol 121 (1420) ◽  
pp. 1012-1014 ◽  
Author(s):  
Kensaku NAKAMURA ◽  
Yoshihiro TAKAHASHI ◽  
Minoru OSADA ◽  
Takumi FUJIWARA
Keyword(s):  
Raman Scattering ◽  
Silicate Glass ◽  
General Expression ◽  
Low Frequency ◽  
Peak Frequency ◽  
Boson Peak ◽  
Binary Silicate

scholarly journals Boson peak, elasticity, and glass transition temperature in polymer glasses: Effects of the rigidity of chain bending

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Naoya Tomoshige ◽  
Hideyuki Mizuno ◽  
Tatsuya Mori ◽  
Kang Kim ◽  
Nobuyuki Matubayasi
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Low Frequency ◽  
Peak Frequency ◽  
Boson Peak ◽  
Polymer Chains ◽  
Coarse Grained ◽  
Elastic Response ◽  
Bending Rigidity

AbstractThe excess low-frequency vibrational spectrum, called boson peak, and non-affine elastic response are the most important particularities of glasses. Herein, the vibrational and mechanical properties of polymeric glasses are examined by using coarse-grained molecular dynamics simulations, with particular attention to the effects of the bending rigidity of the polymer chains. As the rigidity increases, the system undergoes a glass transition at a higher temperature (under a constant pressure), which decreases the density of the glass phase. The elastic moduli, which are controlled by the decrease of the density and the increase of the rigidity, show a non-monotonic dependence on the rigidity of the polymer chain that arises from the non-affine component. Moreover, a clear boson peak is observed in the vibrational density of states, which depends on the macroscopic shear modulus G. In particular, the boson peak frequency ωBP is proportional to $$\sqrt{G}$$G. These results provide a positive correlation between the boson peak, shear elasticity, and the glass transition temperature.

scholarly journals Application of genetic algorithm in extracting cell dielectric characteristics with electrorotation

2019 ◽  
Vol 8 (1) ◽  
pp. 34-39 ◽  
Author(s):  
Elnaz Alizadeh-Haghighi ◽  
Samad Jafarmadar ◽  
Shahram Khalilarya
Keyword(s):  
Genetic Algorithm ◽  
Low Frequency ◽  
Peak Frequency ◽  
Optimization Process ◽  
Low Frequencies ◽  
Dielectric Characteristics ◽  
Medium Conductivity

Abstract In this study the transformed theory is applied to derive the dielectric characteristics of cells, considering the electrorotation (ER) peak frequency. In current studies, estimations of low frequency, which are credible for the values less than 1 mS/m for medium conductivity, are used to obtain the corresponding permittivity and conductivity of cells. Unlike the presented works, the transformed theory applies the comprehensive statement for corresponding permittivity and conductivity of cells. In the transformed theory, the membrane and interior characteristics could be obtained from the high and the low frequencies of peak ER, for all values of conductivity of medium. Characteristics of cells are obtained via optimization of an equation for the conductivity of medium regarding the peak ER frequency. The optimization process is performed applying genetic algorithm due to its swift adaptation to the problem and faster convergence.

scholarly journals Anomalies in the low frequency vibrational density of states for a polymer with intrinsic microporosity – the Boson peak of PIM-1

2018 ◽  
Vol 20 (3) ◽  
pp. 1355-1363 ◽  
Author(s):  
Reiner Zorn ◽  
Huajie Yin ◽  
Wiebke Lohstroh ◽  
Wayne Harrison ◽  
Peter M. Budd ◽  
...  
Keyword(s):  
Density Of States ◽  
Low Frequency ◽  
Boson Peak ◽  
Vibrational Density Of States ◽  
First Time ◽  
Intrinsic Microporosity ◽  
Vibrational Density

For the first time the low frequency vibrational density of states is reported for a polymer with intrinsic microporosity.

scholarly journals Terahertz and Microwave Optical Properties of Single-Crystal Quartz and Vitreous Silica and the Behavior of the Boson Peak

2021 ◽  
Vol 11 (15) ◽  
pp. 6733
Author(s):  
Mira Naftaly ◽  
Andrew Gregory
Keyword(s):  
Single Crystal ◽  
Silica Glass ◽  
Broad Band ◽  
Peak Frequency ◽  
Vitreous Silica ◽  
Peak Height ◽  
Fused Silica ◽  
Boson Peak ◽  
Single Crystal Quartz ◽  
Crystal Quartz

Z-cut single-crystal quartz and vitreous silica (silica glass or fused silica) were evaluated for use as reference materials for terahertz and microwave measurements of complex permittivity, with Z-cut quartz confirmed as being suitable. Measurements of refractive indices and absorption coefficients for o-ray and e-ray in quartz and for vitreous silica are reported at frequencies between 0.2 and 6 THz and at 36 and 144 GHz, and compared with data reported in the literature. A previously unreported broad band was seen in the extraordinary absorption of quartz. The Boson peak in silica glass absorption was examined, and for the first time, two negative relationships have been observed: between the refractive index and the Boson peak frequency, and between the Boson peak height and its frequency.

scholarly journals Earless toads sense low frequencies but miss the high notes

2017 ◽  
Vol 284 (1864) ◽  
pp. 20171670 ◽  
Author(s):  
Molly C. Womack ◽  
Jakob Christensen-Dalsgaard ◽  
Luis A. Coloma ◽  
Juan C. Chaparro ◽  
Kim L. Hoke
Keyword(s):  
High Frequency ◽  
Species Differences ◽  
Low Frequency ◽  
Auditory Brainstem ◽  
Low Frequencies ◽  
Hearing Sensitivity ◽  
Sensory Pathways ◽  
Airborne Sound ◽  
Vibrational Sensitivity ◽  
Species Specific

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

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