A 3D Star Shot to Determine the Gantry, Collimator, and Couch Axes Positions

A linear accelerator has three independent axes that are nominally intersecting at the isocenter. Modern treatment techniques require the coincidence of these axes to lie within a 1‐mm diameter sphere. A solution to verify this requirement is to wrap a film on a cylindrical surface, align the cylinder to the linac's isocenter and gantry axis, and take multiple exposures of slits, rotating either the gantry, collimator, or couch between exposures. The resulting exposure pattern is the 3D equivalent of the 2D star shot and encodes sufficient information to determine each axis’ position in 3D. Moreover, this method uses a single sheet 8“x10” film, a standard film scanner, and a phantom that can be readily built in‐house, making a practical solution to this 3D‐measurement problem

Heat Flux Calculation of PDMS and Silica Aerogel Through Phosphor Thermometry

Phosphor thermometry is an accurate, versatile, and rapid mechanism for inferring temperature information, remotely. The working principle of this technique is based on the different emission characteristics of thermographic phosphors which varies from compound to compound and depends on the specific electronic structure(s) of the phosphor under investigation. Either temporal or spectral composition of the emission characteristics can be used to determine the temperature of the surface that the phosphors are in contact with. In this work thermographic phosphors have been encapsulated in inert transparent or translucent polymers and the behavior of the phosphor-polymer composites was studied as a function of temperature. Silica aerogels and Sylgard184 were chosen for this study and an array of phosphor patches was created on both sides of each material in an off-axis manner. Both aerogels and elastomers are widely used as insulating material but mostly in passive form. Here, the feasibility of imparting sensing capabilities to these materials and potentially measuring heat flux is explored and characterized. Results showed that because of the scattering that occurs in the aerogel material the maximum material thickness that can be accessed by phosphor thermometry is limited to ~ 6 mm, with the setup used in this study. In the case of Sylgard184 an upper limit was not reached. Both up-converting and down converting phosphors were studied. Finally, the performance of thin flexible ceramic films as a thermal buffer was investigated and fully characterized

Remote optical detection of geometrical defects in aerogels and elastomers using phosphor thermometry

Detecting structural damage in the form of geometrical defects in materials that operate under extreme conditions or serve as critical structural components is essential. In this work, the feasibility of using thermographic phosphors as a non-destructive, remote, instantaneous, and customizable sensing mechanism for detection of structural damage was investigated. The two materials studied were (1) Sylgard 184 elastomer and (2) silica aerogels. Two different types of structural damage were investigated in samples of increasing thickness, up to a maximum of 18 mm. To accurately interpret the results, heat flux measurements were also collected from both material types. The changes in the thermal profile of the material as a result of material defects were used to infer information about the structural health of the material. La2O2S:Eu and Mg3F2GeO4:Mn were chosen for the study since their temperature sensitivity range complemented one another and allowed for measurements from cryogenic to 200 °C. It was determined that fracture and failure in both aerogels and Sylgard 184 could be detected by phosphor thermometry and the limit of its resolution was ultimately determined by the thermal properties of the material, the choice of phosphor, and ambient temperature

Flexible thin film ceramics for high temperature thermal sensing applications

Yttria Stabilized Zirconia ceramics have been widely used as protective boundary for high temperature environments and flame shields, intrinsic barrier to moisture, and are often considered for extreme environments. This class of materials has the ability to withstand temperatures up to 3000 °C, far exceeding the maximum temperature of operation for most other materials including polymers. Previously, the design of high performing functional materials involving ceramics was limited due to the bulkiness and lack of flexibility of ceramics. However, with the advent of ultra-thin flexible ceramics, it is possible to create thin layered structures that were not previously possible. In this study the authors investigate the potential of 40 μm thin flexible ceramic strips as flame shields for silica aerogels and polydimethylsiloxane phosphor composites. Results show that thermographic phosphors can be excited across multiple layers of YSZ strips, and, their emission characteristics can be accurately detected across multiple layers. Both decay characteristics and amplitude ratio methods were investigated. The YSZ strips provided thermal protection to both aerogels and elastomers. Embedded thermographic phosphor-based temperature measurements were feasible to a depth of at least 120 μm

Thermal and optical characterization of up-converting thermographic phosphor polymer composite films

Up-converting thermographic phosphors are of significant interest due to specific advantages for temperature measurement applications over traditional contact-based methods. Typically, infrared excitation stimulates visible fluorescence only from the target phosphor and not the surrounding medium. This is in contrast to ultraviolet excitation which may also produce interfering luminescence from cells and other biological tissue in the vicinity, for instance. When traversing a material, usually infrared losses due to scattering and absorption are less than for ultraviolet wavelengths. An example is human skin. This investigation follows logically from earlier efforts incorporating thermographic phosphors into elastomers and aerogels and their function as a reusable temperature sensor has been previously demonstrated by the authors. Layered phosphor/PDMS/aerogel composites are also currently under investigation by the authors for heat flux sensing. For maximum utility and understanding; physical, optical and thermal properties are characterized over a wide range of temperatures. Y2O2S:Yb,Er and La2O2S:Yb,Er up-converting phosphor composites with a fixed doping concentration were synthesized for this study and fully characterized as a function of temperature. The excitation/ emission characteristics of the powder alone and the prepared composites were investigated between -50 °C and +200 °C in an environmental chamber and the decay behavior of each sample type was measured. Here, the authors report on decay behavior and emission intensity of the PDMS composites as a function of temperature. Results were compared with powder -only parameters and are reported here

Thioflavin-T does not report on electrochemical potential and memory of dormant or germinating bacterial spores

ABSTRACT Bacterial spores are metabolically dormant, resistant to microbicides, and vectors of food spoilage and diseases, while germinated spores are easy to kill. Consequently, understanding germination mechanisms may facilitate the development of “germinate-to-eradicate” strategies. Spores germinate in response to many compounds (called germinants). They can also retain the memory of a germinant exposure, such that a second exposure triggers more efficient germination, but how is not clear. A recent high-profile paper [Science (2022) 378:43] suggested that increasing spore electrochemical potential is how memory is “stored” based on measurements of Bacillus subtilis spores’ accumulation of the dye thioflavin-T after germinant exposure. Indeed, we found that wild-type spores of three Bacillus and one Clostridioides species all exhibited this early thioflavin-T accumulation during nutrient pulses. However, our data indicate that inferring spores’ electrochemical potential from thioflavin-T accumulation is problematic. We found that B. subtilis spores lacking their proteinaceous coat exhibited memory but did not accumulate thioflavin-T prior to germinant addition or during nutrient pulses. Furthermore, wild-type Bacillus spores germinating with dodecylamine, which also elicits memory, showed no thioflavin-T accumulation. Finally, we found that thioflavin-T accumulation by a germinating spore is outside the spore core at early stages but inside the spore core as germination proceeds. These findings suggest that thioflavin-T accumulation during the early stages of germination is due to its binding to one or more protein in the spore coat rather than to changes in spores’ electrochemical potential; thus, thioflavin-T is not a potentiometric dye for the study of spore memory of germinant pulses. IMPORTANCE Bacillus and Clostridium spores cause food spoilage and disease because of spores’ dormancy and resistance to microbicides. However, when spores “come back to life” in germination, their resistance properties are lost. Thus, understanding the mechanisms of spore germination could facilitate the development of “germinate to eradicate” strategies. One germination feature is the memory of a pulsed germinant stimulus leading to greater germination following a second pulse. Recent observations of increases in spore binding of the potentiometric dye thioflavin-T early in their germination of spores led to the suggestion that increasing electrochemical potential is how spores “remember” germinant pulses. However, new work finds no increased thioflavin-T binding in the physiological germination of Coatless spores or of intact spores germinating with dodecylamine, even though spore memory is seen in both cases. Thus, using thioflavin-T uptake by germinating spores to assess the involvement of electrochemical potential in memory of germinant exposure, as suggested recently, is questionable