The oral microbiota was compared between Romanian adolescents with a high prevalence of caries and no dental care and Swedish caries-active and caries-free adolescents in caries prevention programs and with a low prevalence of caries. Biofilm samples were analyzed by FLX+ pyrosequencing of the V1 to V4 hypervariable regions of the 16S rRNA gene and polymerase chain reaction (PCR)/quantitative PCR (qPCR) for Streptococcus mutans and Streptococcus sobrinus. Sequences obtained blasted to 9 phyla, 66 genera, and 401 human oral taxa (HOT) in the 16S rRNA Human Oral Microbiome Database, of which 295 were represented by ≥20 sequences. The Romanian adolescents had more sequences in Firmicutes and fewer in Actinobacteria phyla and more sequences in the genera Bacteroidetes [G-3], Porphyromonas, Abiotrophia, Filifactor, Peptostreptococcaceae [11][G-4], Pseudoramibacter, Streptococcus, and Neisseria and fewer in Actinomyces, Selenomonas, Veillonella, Campylobacter, and TM7 [G-1] than the Swedish groups. Multivariate modeling employing HOT, S. sobrinus and S. mutans (PCR/qPCR), and sugar snacks separated Romanian from Swedish adolescents. The Romanian adolescents' microbiota was characterized by a panel of streptococci, including S. mutans, S. sobrinus, and Streptococcus australis, and Alloprevotella, Leptotrichia, Neisseria, Porphyromonas, and Prevotella. The Swedish adolescents were characterized by sweet snacks, and those with caries activity were also characterized by Prevotella, Actinomyces, and Capnocytophaga species and those free of caries by Actinomyces, Prevotella, Selenomonas, Streptococcus, and Mycoplasma. Eight species including Streptococcus mitis and Streptococcus species HOT070 were prevalent in Romanian and Swedish caries-active subjects but not caries-free subjects. In conclusion, S. mutans and S. sobrinus correlated with Romanian adolescents with caries and with limited access to dental care, whereas S. mutans and S. sobrinus were detected infrequently in Swedish adolescents in dental care programs. Swedish caries-active adolescents were typically colonized by Actinomyces, Selenomonas, Prevotella, and Capnocytophaga. Hence, the role of mutans streptococci as a primary caries pathogen appears less pronounced in populations with prevention programs compared to populations lacking caries treatment and prevention strategies.

We calculate the evaporative cooling dynamics of trapped one-dimensional Bose-Einstein condensates for parameters leading to a range of condensates and quasicondensates in the final equilibrium state. We confirm that solitons are created during the evaporation process, but always eventually dissipate during thermalisation. The distance between solitons at the end of the evaporation ramp matches the coherence length in the final thermal state. Calculations were made using the classical fields method. They bridge the gap between the phase defect picture of the Kibble-Zurek mechanism and the long-wavelength phase fluctuations in the thermal state. The quasi-one-dimensional (1D) Bose gas in elongated clouds of neutral ultra-cold atoms[1, 2] differs markedly from the Bose-Einstein condensate (BEC) in three-dimensional geometries. One of the most remarkable features is the presence of two characteristic temperatures when the trapped gas is cooled [2]. Below T c , the lowest mode becomes appreciably occupied[8] but the phase coherence length l φ ∝ 1/T is smaller than the size of the system. This is called a quasicondensate. Below a second temperature T φ , l φ grows to the size of the cloud, and the state is a true BEC. The phase coherence in these states have been extensively studied both experimentally [3,4] and theoretically [2,[5][6][7][8][9].In thermal equilibrium, the variance in phase and onebody density matrix have been calculated [2,5,9,10]. Their short-range behaviour gives the phase correlation length l φ near the center of the trap:In equilibrium, the phase in a single experimental realisation varies smoothly over length scales l φ [10]. On the other hand, phase fluctuations have also been predicted from the Kibble-Zurek mechanism[11] (KZM) after the onset of condensation, when the system is far from equilibrium. These fluctuations are seemingly different in nature than those discussed above. During evaporative cooling, phase defects in the form of grey solitons appear when crossing the characteristic temperature T c . They are born when local condensation occurs faster than distant regions can communicate to agree on a common phase. When the expanding initial phase domains meet, soliton defects form on the interfaces between them. Therefore, during the formation of a condensate the phase experiences sudden jumps at the temporal position of every soliton, and phase domains appear between them of a size equal to the separation between neighbouring solitons. A natural question arises whether these pre-formed domains are somehow related to the phase fluctuations in equilibrium. The aim of this paper is to show how the phase fluctuations in these two cases are connected.The number of solitons while crossing T c has been predicted as a function of the quench rate [6]. A calculation where chemical potential was quenched at T = 0 demonstrated the KZM for a uniform gas [7]. Here we show that the Kibble-Zurek scaling also applies for a realistic model of evaporative cooling in a trap. We have simulated the non-equil...

We show that the phase of a condensate in a finite temperature gas spreads linearly in time at long times rather than in a diffusive way. This result is supported by classical field simulations, and analytical calculations which are generalized to the quantum case under the assumption of quantum ergodicity in the system. This super-diffusive behavior is intimately related to conservation of energy during the free evolution of the system and to fluctuations of energy in the prepared initial state.

We show that, at finite temperature, the maximum spin squeezing achievable using interactions in Bose-Einstein condensates has a finite limit when the atom number N→∞ at fixed density and interaction strength. We calculate the limit of the squeezing parameter for a spatially homogeneous system and show that it is bounded from above by the initial noncondensed fraction.