The immune response to malaria in utero.

Malaria causes tremendous early childhood morbidity and mortality, providing an urgent impetus for the development of a vaccine that is effective in neonates. However, the infant immune response to malaria may be influenced by events that occur well before birth. Placental malaria infection complicates one quarter of all pregnancies in Africa and frequently results in exposure of the fetus to malaria antigens in utero, while the immune system is still developing. Some data suggest that in utero exposure to malaria may induce immunologic tolerance that interferes with the development of protective immunity during childhood. More recently, however, a growing body of evidence suggests that fetal malaria exposure can prime highly functional malaria-specific T- and B-cells, which may contribute to postnatal protection from malaria. In utero exposure to malaria also impacts the activation and maturation of fetal antigen presenting cells and innate lymphocytes, which could have implications for global immunity in the infant. Here, we review recent advances in our understanding of how various components of the fetal immune system are altered by in utero exposure to malaria, discuss factors that may tilt the critical balance between tolerance and adaptive immunity, and consider the implications of these findings for malaria prevention strategies

Characterisation of Nitinol for the Design of Tuneable Transducers

No abstract available

Nitinol Cymbal Transducers for Power Ultrasonics Applications

The effects of shape memory alloy phenomena such as superelasticity and thermal phase change on the dynamic response of a cymbal transducer incorporating two Nitinol end-caps has not been studied into detail. The experimental results, using both vibration response and electrical impedance measurements, demonstrate that the use of Nitinol as the end-cap material for a cymbal transducer can impose significant effects on the vibration response. The understanding of the effect Nitinol has on the vibration response of a cymbal transducer provides future opportunities to design a power ultrasonic cymbal transducer that can operate with two different and selectable vibration behaviours, which is particularly appealing in a range of applications, including ultrasonic cutting devices that are required to penetrate more than one material

A comparison of two configurations for a dual-resonance cymbal transducer

The ability to design tuned ultrasonic devices that can be operated in the same mode at two different frequencies has the potential to benefit a range of applications, such as surgical cutting procedures where the penetration through soft then hard tissues could be enhanced by switching the operating frequency. The cymbal transducer has recently been adapted to form a prototype ultrasonic surgical cutting device that operates at a single frequency. In this paper, two different methods of configuring a dual-resonance cymbal transducer are detailed. The first approach relies on transducer fabrication using different metals for the two end-caps, thereby forming a dual-resonance transducer. The second employs transducer end-caps composed from a shape memory alloy, superelastic Nitinol. The resonance frequency of the Nitinol transducer depends on the phase microstructure of the material, switchable through the temperature and/or stress dependency of the Nitinol end-caps. The vibration response of each transducer is measured through electrical impedance measurements and laser Doppler vibrometry, and finite element analysis is used to show the sensitivity of transducer modal response to the fabrication processes. Through this research, two viable dual-resonance cymbal transducers are designed and characterised, and compared to illustrate the advantages and disadvantages of the two different approaches

Dynamics characterisation of cymbal transducers for power ultrasonics applications

A class V cymbal flextensional transducer is composed of a piezoceramic disc sandwiched between two cymbal-shaped shell end-caps. Depending on the type of piezoceramic, there exists a maximum voltage that can be reached without depolarisation, but also, at higher voltage levels, amplitude saturation can occur. In addition, there is a restriction imposed by the mechanical strength of the bonding agent. The effects of input voltage level on the vibration response of two cymbal transducers are studied. The first cymbal transducer has a standard configuration of end-caps bonded to a piezoceramic disc, whereas the second cymbal transducer is a modified design which includes a metal ring to improve the mechanical coupling with the end-caps, to enable the transducer to operate at higher voltages, thereby generating higher displacement amplitudes. This would allow the transducer to be suitable for power ultrasonics applications. Furthermore, the input voltages to each transducer are increased incrementally to determine the linearity in the dynamic responses. Through a combination of numerical modelling and experiments, it is shown how the improved mechanical coupling in the modified cymbal transducer allows higher vibration amplitudes to be reached

Optimisation of a cymbal transducer for its use in a high-power ultrasonic cutting device for bone surgery

The class V cymbal is a flextensional transducer commonly used in low-power ultrasonic applications. The resonance frequency of the transducer can be tailored by the choice of end-cap and driver materials, and the dimensions of the end-caps. The cymbal transducer has one significant limitation which restricts the operational vibration amplitude of the device. This is the limit imposed by the mechanical strength of the bonding agent between the metal end-cap and the piezoceramic driver. Therefore, when there is an increase in the input power or displacement, the stresses in the bonding layer can lead to debonding, thereby rendering the cymbal transducer ineffective for high-power ultrasonic applications. In this paper, several experimental analyses have been performed, complemented by the use of Abaqus/CAE finite element analysis, in order to develop a high-power ultrasonic cutting device for bone surgery using a new configuration of cymbal transducer, which is optimised for operation at high displacement and high input power. This new transducer uses a combination of a piezoceramic disc with a metal ring as the driver, thereby improving the mechanical coupling with the metal end-cap

Differential Scanning Calorimetry of Superelastic Nitinol for Tuneable Devices

Nitinol has been used to fabricate tuneable-frequency cymbal transducers by exploiting its solid-state phase transformation capability. The temperatures at which Nitinol transforms are commonly measured using differential scanning calorimetry (DSC). However, these measurements are shown to be inaccurate for superelastic Nitinol, reportedly attributed to residual stresses in the material resulting from the fabrication process. This study of DSC accuracy is conducted for untreated and heat-treated superelastic Nitinol. Cymbal transducers are fabricated from both materials and it is demonstrated, through comparison of results from DSC estimations of transformation temperatures with the vibration response measured through a heating cycle, that heat-treated superelastic Nitinol can be accurately characterised by DSC

Nitinol Cymbal Transducers for Power Ultrasonics Applications

The effects of shape memory alloy phenomena such as superelasticity and thermal phase change on the dynamic response of a cymbal transducer incorporating two Nitinol end-caps has not been studied into detail. The experimental results, using both vibration response and electrical impedance measurements, demonstrate that the use of Nitinol as the end-cap material for a cymbal transducer can impose significant effects on the vibration response. The understanding of the effect Nitinol has on the vibration response of a cymbal transducer provides future opportunities to design a power ultrasonic cymbal transducer that can operate with two different and selectable vibration behaviours, which is particularly appealing in a range of applications, including ultrasonic cutting devices that are required to penetrate more than one material

Smart cymbal transducers with nitinol end caps tunable to multiple operating frequencies

Cymbal flextensional transducers have principally been adopted for sensing and actuation and their performance in higher power applications has only recently been investigated. Nitinol is a shape-memory alloy (SMA) with excellent strain recovery, durability, corrosion resistance, and fatigue strength. Although it has been incorporated in many applications, the implementation of nitinol, or any of the SMAs, in power ultrasonic applications is limited. Nitinol exhibits two phenomena, the first being the superelastic effect and the second being the shape-memory effect (SME). This paper assesses two cymbal transducers, one assembled with superelastic nitinol end caps and the other with shape-memory nitinol end caps. Characterization of the nitinol alloy before the design of such transducers is vital, so that they can be tuned to the desired operating frequencies. It is shown this can be achieved for shape-memory nitinol using differential scanning calorimetry (DSC); however, it is also shown that characterizing superelastic nitinol with DSC is problematic. Two transducers are assembled whose two operating frequencies can be tuned, and their dynamic behaviors are compared. Both transducers are shown to be tunable, with limitation for high-power applications largely being associated with the bond layer