196,303 research outputs found
Osservazioni su riproduzione e sviluppo larvale di Desdemona ornata (Polychaeta: Sabellidae).
No full textReproductive biology and larval development of the polychaete Desdemona ornata (Banse) (Sabellidae) is described in a population collected in a brackish habitat of the Elba island. D. ornata is a gonochoric species, mature eggs measured 132x66 microns. Embryos and larvae are brooded in the maternal tube. larvae hatched at 3 setigerous segment
A portable laser system for high-precision atom interferometry experiments
No full textWe present a modular rack-mounted laser system for the cooling and manipulation of neutral rubidium atoms which has been developed for a portable gravimeter based on atom interferometry that will be capable of performing high-precision gravity measurements directly at sites of geophysical interest. This laser system is constructed in a compact and mobile design so that it can be transported to different locations, yet it still offers improvements over many conventional laboratory-based laser systems. Our system is contained in a standard 19" rack and emits light at five different frequencies simultaneously on up to 12 fibre ports at a total output power of 800 mW. These frequencies can be
changed and switched between ports in less than a microsecond. The setup includes two phase-locked diode lasers with a phase noise spectral density of less than 1 μrad/Hz1/2 in the frequency range in which our gravimeter is most sensitive to noise. We characterise this laser system and evaluate the performance limits it imposes on an interferomete
Precision measurement of the Newtonian gravitational constant using cold atoms
No full textAbout 300 experiments have tried to determine the value of the Newtonian gravitational constant, G, so far, but large discrepancies in
the results have made it impossible to know its value precisely. The
weakness of the gravitational interaction and the impossibility of
shielding the effects of gravity make it very difficult to measure G while
keeping systematic effects under control. Most previous experiments
performed were based on the torsion pendulum or torsion balance
scheme as in the experiment by Cavendish in 1798, and in all cases
macroscopic masses were used. Here we report the precise determination of G using laser-cooled atoms and quantum interferometry.
We obtain the value G = 6.67191(99) 10^-11 m^3 kg^-1 s^-2 with a relative uncertainty of 150 parts per million (the combined standard
uncertainty is given in parentheses). Our value differs by 1.5 com-
bined standard deviations from the current recommended value of
the Committee on Data for Science and Technology. A conceptually different experiment such as ours helps to identify the systematic errors that have proved elusive in previous experiments, thus
improving the confidence in the value of G. There is no definitive
relationship between G and the other fundamental constants, and
there is no theoretical prediction for its value, against which to test
experimental results. Improving the precision with which we know
G has not only a pure metrological interest, but is also important
because of the key role that G has in theories of gravitation, cosmology, particle physics and astrophysics and in geophysical models
Hyperfine splitting of [Al VI] 3.66 mu m and the Al isotopic ratio in NGC 6302
No full textThe core of planetary nebula NGC 6302 is filled with high-excitation photoionized gas at low expansion velocities. It represents a unique astrophysical situation in which to search for hyperfine structure (HFS) in coronal emission lines from highly ionized species. HFS is otherwise blended by thermal or velocity broadening. Spectra containing [Al vr] 3.66 mu m P-3(2) <- P-3(1), obtained with Phoenix on Gemini South at resolving powers of up to 75000, resolve the line into five hyperfine components separated by 20-60 km s(-1) as a result of the coupling of the I = 5/2 nuclear spin of Al-27 with the total electronic angular momentum J. The isotope Al-26 has a different nuclear spin of I = 5, and a different HFS, which allows us to place a 3 sigma upper limit on the Al-26/Al-27 abundance ratio of 1/33. We measure the HFS magnetic dipole coupling constants for [Al vr], and provide the first estimates of the electric quadrupole HFS coupling constants obtained through astronomical observations of an atomic transition
Precision Measurement of Gravity with Cold Atoms in an Optical Lattice and Comparison with a Classical Gravimeter
No full textWe report on a precision measurement of gravitational acceleration using ultracold strontium atoms confined in an amplitude-modulated vertical optical lattice. An uncertainty dg/g ~ 10^-7 is reached by measuring at the 5th harmonic of the Bloch frequency. The value obtained with this microscopic quantum system is consistent with the one measured with a classical gravimeter. Using lattice modulation to prepare the atomic sample, we also achieve high visibility of Bloch oscillations for ~20 s. These results can be of relevance for testing gravitational redshift and Newtonian law at micrometer scale
Determination of the Newtonian Gravitational Constant Using Atom Interferometry
No full textWe present a new measurement of the Newtonian gravitational constant G based on cold atom interferometry. Freely falling samples of laser-cooled rubidium atoms are used in a gravity gradiometer to probe the field generated by nearby source masses. In addition to its potential sensitivity, this method is intriguing as gravity is explored by a quantum system. We report a value of G = 6.667 · 10^(−1)1 m^3 kg^(−1) s^(−2), estimating a statistical uncertainty of
±0.011 · 10^(−11) m^3 kg^(−1) s^(−2) and a systematic uncertainty of
±0.003 · 10^(−11) m^3 kg^(−1) s^(−2). The long-term stability of the instrument
and the signal-to-noise ratio demonstrated here open interesting perspectives for pushing the measurement accuracy below the 100 ppm level
Measurement of the Gravity-Field Curvature by Atom Interferometry
No full textWe present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by
the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of
using such a scheme for a new determination of the Newtonian constant of gravity is also discussed
Response to Tilic and Bartolomaeus's Commentary on the original Research Paper “Unravelling the ultrastructure and mineralogical composition of fireworm stinging bristles” (Zoology, 144)
No full textIn their Commentary to our paper recently published in Zoology (Righi et al., 2021a), Tilic and Bartolomaeus question our findings that the chaetae of Hermodice carunculata (Annelida) are hollow and able to store and deliver venoms. They sustain the idea that inflammatory chemicals are secreted through epidermal glands and possibly exposed to predator trough wounds caused by the brittle chaetae. We provide evidence-based arguments in support of our considerations. The sample preparation procedures did not affect the native inner structure of unfixed fireworm chaetae, which is clearly hollow as supported by both ultrastructure observation and crystal-chemical analysis of constituents. Furthermore, our previous and more recent feeding bioassays and chemical analysis indicate both that chaetae retain strong deterrent capacities even when isolated from the body of H. carunculata, and that they contain venoms. The cellular mechanisms involved in fireworm chaeta storage and deliver of chemicals are still unstudied. We strongly believe that this lack of knowledge should draw further attention on H. carunculata biology, pursuing new hypotheses and studies based on the noteworthy information which has been obtained so far
Unravelling the ultrastructure and mineralogical composition of fireworm stinging bristles
No full textAmphinomid fireworms are notorious for their stinging dorsal bristles (notochaetae), but it is still unclear whether the irritation they cause is merely mechanical or if the notochaetae contain toxins. Furthermore, although fireworm chaetae have always been described as calcareous, their composition has never been investigated to date and strong debates are ongoing on their internal structure. Unravelling the native ultrastructure and composition of fireworm chaetae is the first crucial step to assess whether the hypothesis of toxin vehiculation could be fully considered. We examined for the first time the chemical and mineralogical composition, the ultrastructure and the external structure of the dorsal and ventral chaetae of the large species Hermodice carunculata. All the measurements were carried out on samples prepared without the use of chemical reagents, except for those targeted to investigate if decalcification altered the ultrastructure of the chaetae. A crystal-chemical strategy, combining chemical, diffraction and thermal analyses clearly showed the occurrence of crystalline calcium carbonate and clusters of phosphatic amorphous material. Scanning electron micrographs and energy dispersive X-ray measurements showed that the dorsal chaetae have an extremely shallow insertion point in the body respect to the ventral chaetae, that could facilitate the release of the notochaetae in the environment. Their proximal part is characterized by canals with a hexagonal pattern rich in Ca and P, followed by a large cavity upwards. The harpoon-shaped ends and the central canals of the notochaetae completely disappeared after exposure to EDTA. The notochaetae are hollow and may be able to vehicle toxins. The absence of the honeycomb pattern in the distal part of the notochaetae and their slenderness probably contribute to their brittleness and high sensitivity to breakage on contact. These observations constitute keystone understandings to shed light on fireworm defensive and offensive capacities and their ecological success
Analisi preliminari sulla tossicità di essudati di Arenicola marina (Linnaeus, 1758) (Annelida: Arenicolidae)
No full textThe effects of the exudate (crude and its organic extracts) obtained by Arenicola marina
(Annelida: Arenicolidae) were evaluated through acute toxicity bioassays on the annelid Dinophilus
gyrociliatus. Preliminary chemical analyses were also performed. The exudate and its n-buthanol
extract were toxic (LC50 24h=12%, c.i.=9.7-14.7% and 31.7 mg l-1, c.i.=27.9-36 mg l-1, respectively). The
results support the hypothesis that the exudate could be involved in the chemical defence of A. marina
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