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American Society for Testing and Materials

Bioceramics of calcium orthophosphates

Ionic substitutions in calcium phosphates synthesized at low temperature.

The present overview is intended to point the readers’ attention to the important subject of calcium orthophosphates. These materials are of the special significance because they represent the inorganic part of major normal (bones, teeth and dear antlers) and pathological ( i.e. those appearing due to various diseases) calcified tissues of mammals. Due to a great chemical similarity with the biological calcified tissues, many calcium orthophosphates possess remarkable biocompatibility and bioactivity. Materials scientists use this property extensively to construct artificial bone grafts that are either entirely made of or only surface-coated with the biologically relevant calcium ortho-phosphates. For example, self-setting hydraulic cements made of calcium orthophosphates are helpful in bone repair, while titanium substitutes covered by a surface layer of calcium orthophosphates are used for hip joint endoprostheses and as tooth substitutes. Porous scaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. In addition, technical grade calcium orthophosphates are very popular mineral fertilizers. Thus ere calcium orthophosphates are of great significance for humankind and, in this paper, an overview on the current knowledge on this subject is provided.

https://www.mdpi.com/1996-1944/2/2/399/pdf

Calcium Orthophosphates in Nature, Biology and Medicine

Silicon substitution in the calcium phosphate bioceramics

Synthesis and characterization of single-phase silicon-substituted α-tricalcium phosphate

Two methods for low‐altitude calibration of a single‐rotor unmanned aircraft system using a real‐time compensator are tested: (1) a stationary calibration where the unmanned aircraft system executes manoeuvres while hovering in order to minimize ambient field changes due to the local geology; and (2) an adapted box calibration flown in four orthogonal directions. Both methods use two compensator‐specific limits derived from established methods for manned airborne calibration: the lowest frequency used by the compensator for the calibration algorithm and the maximum variation of the ambient magnetic intensity experienced by the unmanned aircraft system during calibration. Prior to flying, the unmanned aircraft system was magnetically characterized using the heading error and fourth difference. Magnetic interference was mitigated by extending the magnetometer‐unmanned aircraft system separation distance to 1.7 m, shielding, and demagnetization. The stationary calibration yielded an improvement ratio of 8.595 and a standard deviation of the compensated total magnetic intensity of 0.075 nT (estimated Figure‐of‐Merit of 3.8 nT). The box calibration also yielded an improvement ratio of 3.989 and a standard deviation of the compensated total magnetic intensity of 0.083 nT (estimated Figure‐of‐Merit of 4.2 nT). The stationary and box calibration solutions were robust with low cross‐correlation indexes (1.090 and 1.048, respectively) when applied to a non‐native data set.

Real-time compensation of magnetic data acquired by a single-rotor unmanned aircraft system

One of the barriers preventing unmanned aircraft systems (UASs) from having a larger presence in the geophysical magnetic surveying industry is the magnetic interference generated by the UAS and it...

Magnetic interference testing method for an electric fixed-wing unmanned aircraft system (UAS)

Ultrasonically accelerated dissolution of multiphase silicon stabilized tricalcium phosphate powders in water or Earle's balanced salt solution transforms the powders into needle-like calcium deficient apatite crystals with the c-axis (001) oriented along the needle. Ion exchange with the solution occurs primarily in the first hours of immersion. The transformation is driven by an interaction between the crystal surface and adsorbed water leading to the growth of crystallites which have the most stable surface configuration. First principles calculations of the surface energies of various hydroxyapatite surfaces with and without adsorbed water shows that depending on the ion concentrations in the fluid that determine the chemical potential of tricalcium phosphate, either Ca-rich (010) or stoichiometric (001) layers are the dominant surfaces. The higher the chemical potential, the more elongated in the (001) direction the crystallites become to minimize the total surface energy. The loss of a calcium Ca(2+) compensated by the addition of two H(+) is strongly favoured energetically on the (001) and Ca-rich (010) surfaces. A high concentration of excess Si at grain boundaries may be partly responsible for the rapid transformation of multiphase Si-TCP.

/pdf/dissolution-and-re-crystallization-processes-in-multiphase-2u86f10gi9.pdf

Dissolution and re-crystallization processes in multiphase silicon stabilized tricalcium phosphate

. Magnetic interference source identification is a critical preparation step
for magnetometer-mounted unmanned aircraft systems (UAS) used for
high-sensitivity geomagnetic surveying. A magnetic field scanner was built
for mapping the low-frequency interference that is produced by a UAS. It was
used to compare four types of electric-powered UAS capable of carrying an
alkali-vapour magnetometer: (1) a single-motor fixed-wing, (2) a
single-rotor helicopter, (3) a quad-rotor helicopter, and (4) a hexa-rotor
helicopter. The scanner's error was estimated by calculating the
root-mean-square deviation of the background total magnetic intensity over
the mapping duration; averaged values ranged between 3.1 and 7.4 nT. Each
mapping was performed above the UAS with the motor(s) engaged and with the
UAS facing in two orthogonal directions; peak interference intensities
ranged between 21.4 and 574.2 nT. For each system, the interference is a
combination of both ferromagnetic and electrical current sources. Major
sources of interference were identified such as servo(s) and the cables
carrying direct current between the motor battery and the electronic speed
controller. Magnetic intensity profiles were measured at various motor
current draws for each UAS, and a change in intensity was observed for
currents as low as 1 A.

/pdf/magnetic-interference-mapping-of-four-types-of-unmanned-537un17me8.pdf

L. Tuck

Papers

Synthesis and characterization of single-phase silicon-substituted α-tricalcium phosphate

Real-time compensation of magnetic data acquired by a single-rotor unmanned aircraft system

Magnetic interference testing method for an electric fixed-wing unmanned aircraft system (UAS)

Dissolution and re-crystallization processes in multiphase silicon stabilized tricalcium phosphate

Magnetic interference mapping of four types of unmanned aircraft systems intended for aeromagnetic surveying