Numerical simulation plays an important role in the study of structure
formation of the universe. However, the mass resolution in current simulations
is still poor. Due to technical difficulties, it is necessary to use both
greatly reduced number density of particles and greatly raised unit particle
mass. Consequently, the particle masses used in cosmological simulations are
about $10^{70}$ times larger than the $Gev$ candidates in particle physics.
This is a huge physical bias that cannot be neglected when interpreting the
results of the simulations. Here we discuss how such a bias affects Cold Dark
Matter (CDM) cosmological simulations. We find that the small scale properties
of the CDM particle system are changed in two aspects. 1) An upper limit is
imposed on the spatial resolution of the simulation results. 2) Most
importantly, an unexpected short mean free path is produced, and the
corresponding two body scattering cross section is close to the value expected
in the Self-Interaction Dark Matter(SIDM) model. Since the mean free path of
real CDM particle systems is much longer than that in the simulations, our
results imply 1) that there is probably no 'cusp problem' in real CDM halos,
and 2) that a much longer time is needed to form new virialized halos in real
CDM particle systems than in the simulations. This last result can help us
understand the 'substructure problem'. Our discussion can also explain why the
massive halos in the simulations may have smaller concentration coefficients.Comment: 4 pages,no figures. Submitted to ApJ
This vitro study aimed to evaluate the effects of 45S5 bioactive glass (BAG) and Er: YAG laser as desensitization treatments on the microtensile bond strength (MTBS) of fluorosed teeth. The 120 noncarious fluorosis were to obtain superficial dentin, being classified into four groups according to the Thylstrup and Fejerskov Index (TFI). Specimens from each group were randomly divided into five subgroups. After fluorosed teeth hypersensitivity models were established, the following pretreatments were applied on dentine surface: Subgroup 1: deionized water (Control); Subgroup 2: BAG; Subgroup 3: Er:YAG laser; Subgroup 4: BAG + Er:YAG laser, and Subgroup 5: Er:YAG laser + BAG. One sample was randomly selected from each subgroup for scanning electron microscope (SEM). The remaining samples were bonded with composite resin by Adper Single Bond 2 adhesive. Then water bath at 37 C for 24 hr. After 5,000 thermocycling, MTBS was tested and fracture mode was analyzed. The difference of MTBS between BAG group and Control group was found statistically significant (p < .05) in fluorosis. The Er:YAG laser + BAG group showed lowest MTBS values in fluorosis. In conclusion, the pretreatment of BAG might be beneficial to the adhesive of fluorosed teeth. Er:YAG laser desensitization alone or using BAG first and then Er:YAG laser desensitization might not affect the adhesive of fluorosed teeth, while Er:YAG laser desensitization followed by the pretreatment of BAG would be not conducive to the adhesive of fluorosed teeth.
The study evaluated the effect of sodium hypochlorite (NaOCl) treatment on fluorotic enamel bonding of four adhesive systems. They were Single Bond 2 (SB2), Prime&Bond NT (PBN), Clearfil SE Bond (CSB), and Single Bond Universal (SBU). One hundred eighteen extracted moderate fluorotic molars were divided into eight groups according to NaOCl pretreatment and four adhesive systems. The microshear bond strength (μSBS), etching pattern, and penetration depth (PD) were observed. The statistical method was two-way ANOVA and least significant difference (LSD) test (α=0.05). The application of NaOCl significantly increased the μSBS of PBN and SBU (p<0.05). The enamel-etching pattern of CSB and SBU was deeper under SEM. A noticeable increase of PD was in SB2 and SBU after the application of NaOCl (p<0.05). Pretreatment of 5.25% NaOCl for the 60 s can increase μSBS of PBN and SBU, PD of SB2 and SBU, and improve enamel-etching pattern of CSB and SBU to fluorotic enamel.
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