Shifting beams at normal incidence via controlling momentum-space geometric phases

When hitting interfaces between two different media, light beams may undergo small shifts. Such beam shifts cannot be described by the geometrical optics based on Snell’s law and their underlying physics has attracted much attention. Conventional beam shifts like Goos-Hänchen shifts and Imbert-Fedorov shifts not only require obliquely incident beams but also are mostly very small compared to the wavelength and waist size of the beams. Here we propose a method to realize large and controllable polarization-dependent lateral shifts for normally incident beams with photonic crystal slabs. As a proof of the concept, we engineer the momentum-space geometric phase distribution of a normally incident beam by controlling its interaction with a photonic crystal slab whose momentum-space polarization structure is designed on purpose. The engineered geometric phase distribution is designed to result in a large shift of the beam. We fabricate the designed photonic crystal slab and directly observe the beam shift, which is ~5 times the wavelength and approaches the waist radius. Based on periodic structures and only requiring simple manipulation of symmetry, our proposed method is an important step towards practical applications of beam shifting effects.

Experimental determination of IGV preswirl effect on impeller blade vibration in an unshrouded centrifugal compressor

The unshrouded impeller is widely used in industrial centrifugal compressors and normally operates at high tip speed and large volume flow. However, this type of impeller can be very sensitive to flow excitations such as IGV wake, and hence encounters the challenge of high dynamic stress. Due to the lack of experimental vibration data, this paper aims to enhance the understanding of the IGV preswirl effect. The real operating representative data from strain gauges is acquired during the experiment. The blade transient and quasi-steady response due to upstream IGV wake under different configurations are investigated and quantified. Results show that the blade response increases with larger positive regulation. And under specific operating conditions, the vibration of the blade is quite large, which is comparable with synchronize resonance. This increment is attributed to the aerodynamic loading change due to enhanced distortion of the inlet flow. Based on the current findings, accurate numerical prediction of the blade forced vibration for a large shift of inlet flow condition is also needed for more reliable operating of the impeller.

4D printing of reconfigurable metamaterials and devices

Shape-shifting materials are a powerful tool for the fabrication of reconfigurable materials. Upon activation, not only a change in their shape but also a large shift in their material properties can be realized. As compared with the 4D printing of 2D-to-3D shape-shifting materials, the 4D printing of reconfigurable (i.e., 3D-to-3D shape-shifting) materials remains challenging. That is caused by the intrinsically 2D nature of the layer-by-layer manner of fabrication, which limits the possible shape-shifting modes of 4D printed reconfigurable materials. Here, we present a single-step production method for the fabrication and programming of 3D-to-3D shape-changing materials, which requires nothing more than a simple modification of widely available fused deposition modeling (FDM) printers. This simple modification allows the printer to print on curved surfaces. We demonstrate how this modified printer can be combined with various design strategies to achieve high levels of complexity and versatility in the 3D-to-3D shape-shifting behavior of our reconfigurable materials and devices. We showcase the potential of the proposed approach for the fabrication of deployable medical devices including deployable bifurcation stents that are otherwise extremely challenging to create.

Tuning network topology and vibrational mode localization to achieve ultralow thermal conductivity in amorphous chalcogenides

Amorphous chalcogenide alloys are key materials for data storage and energy scavenging applications due to their large non-linearities in optical and electrical properties as well as low vibrational thermal conductivities. Here, we report on a mechanism to suppress the thermal transport in a representative amorphous chalcogenide system, silicon telluride (SiTe), by nearly an order of magnitude via systematically tailoring the cross-linking network among the atoms. As such, we experimentally demonstrate that in fully dense amorphous SiTe the thermal conductivity can be reduced to as low as 0.10 ± 0.01 W m−1 K−1 for high tellurium content with a density nearly twice that of amorphous silicon. Using ab-initio simulations integrated with lattice dynamics, we attribute the ultralow thermal conductivity of SiTe to the suppressed contribution of extended modes of vibration, namely propagons and diffusons. This leads to a large shift in the mobility edge - a factor of five - towards lower frequency and localization of nearly 42% of the modes. This localization is the result of reductions in coordination number and a transition from over-constrained to under-constrained atomic network.

Partisan Bias, Economic Expectations, and Household Spending

The well-documented rise in political polarization among the U.S. electorate over the past 20 years has been accompanied by a substantial increase in the effect of partisan bias on survey-based measures of economic expectations. Individuals have a more optimistic view on future economic conditions when they are more closely affiliated with the party that controls the White House, and this tendency has increased significantly over time. Individuals report a large shift in economic expectations based on partisan affiliation after the 2008 and 2016 elections, but administrative data on spending shows no effect of these shifts on actual household spending.

Large shift of the Pacific Walker Circulation across the Cenozoic

<p>Fluctuations in the Pacific Walker circulation (PWC), a zonally-oriented overturning cell across the tropical Pacific, can cause widespread climatic and biogeochemical perturbations. It remains unknown how the PWC developed during the Cenozoic era, with its substantial changes in greenhouse gases and continental positions. Through a suite of coupled model simulations on tectonic timescales, we demonstrate that the PWC was ~38º broader and ~5% more intense during the Early Eocene relative to present. As the climate cooled from the Early Eocene to the Late Miocene, the width of the PWC shrank, accompanied by an increase in intensity that was tied to the enhanced Pacific zonal temperature gradient. However, the locations of the western and eastern branches behave differently from the Early Eocene to the Late Miocene, with the western edge remained steady with time due to the relatively stable geography of the western tropical Pacific; the eastern edge migrates westward with time as the South American continent moves northwest. A transition occurs in the PWC between the Late Miocene and Late Pliocene, manifested by an eastward shift (both the western and eastern edges migrate eastward by >12º) and weakening (by ~22%), which we show here is linked with the closure of the tropical seaways. Moreover, our results suggest that rising CO<sub>2</sub> favors a weaker PWC under the same land-sea configurations, a robust feature across the large spread of Cenozoic climates considered here, supporting a weakening of the PWC in a warmer future.</p>

4D printing of reconfigurable metamaterials and devices

Shape-shifting materials are a powerful tool for the fabrication of reconfigurable materials. Upon activation, not only a change in their shape but also a large shift in their material properties can be realized. As compared with the 4D printing of 2D-to-3D shape-shifting materials, the 4D printing of reconfigurable (i.e., 3D-to-3D shape-shifting) materials remains challenging. That is caused by the intrinsically 2D nature of the layer-by-layer manner of fabrication, which limits the possible shape-shifting modes of 4D printed reconfigurable materials. Here, we present a novel single-step production method for the fabrication and programming of 3D-to-3D shape-changing materials, which requires nothing more than a simple modification of widely available fused deposition modeling (FDM) printers. This simple modification allows the printer to print on curved surfaces. We demonstrate how this modified printer can be combined with novel design strategies to achieve unprecedented levels of complexity and versatility in the 3D-to-3D shape-shifting behavior of our reconfigurable materials and devices. We showcase the potential of the proposed approach for the fabrication of deployable medical devices including deployable bifurcation stents that are otherwise extremely challenging to create.

Ultralow thermal conductivity via topological network control of vibrational localization in amorphous chalcogenides

Amorphous chalcogenide alloys are key materials for data storage and energy scavenging applications due to their large non-linearities in optical and electrical properties as well as low vibrational thermal conductivities. Here, we report on a mechanism to suppress the thermal transport in a representative amorphous chalcogenide system, silicon telluride (SiTe), by nearly an order of magnitude via systematically tailoring the cross-linking network among the atoms. As such, we experimentally demonstrate that in fully dense amorphous SiTe the thermal conductivity can be reduced to as low as 0.1 ± 0.01 W/m/K for high tellurium content with a density nearly twice that of amorphous silicon. Using ab-initio simulations integrated with lattice dynamics, we attribute the ultralow thermal conductivity of SiTe to the suppressed contribution of extended modes of vibration, namely propagons and diffusons. This leads to a large shift in the mobility edge - a factor of five - towards lower frequency and localization of nearly 42% of the modes. This localization is the result of reductions in coordination number and a transition from over-constrained to underconstrained atomic network.

Oral and Intravenous Iron Therapy Differentially Alter The on- and Off-Tumour Microbiota in Anaemic Colorectal Cancer Patients.

Background Iron deficiency anaemia is a common complication of colorectal cancer and may require iron therapy. Oral iron can increase iron available to gut bacteria and may alter the colonic microbiota. We performed an intervention study to compare oral and intravenous iron therapy on the colonic tumour-associated (on-tumour) and paired non-tumour-associated adjacent (off-tumour) microbiota. Anaemic patients with colorectal adenocarcinoma received either oral ferrous sulphate (n=16) or intravenous ferric carboxymaltose (n=24). On- and off-tumour biopsies were obtained post-surgery and microbial profiling was performed using 16S ribosomal RNA analysis.Results Off-tumour α- and β-diversity were significantly different between iron treatment groups. No differences in on-tumour diversity were observed. Off-tumour microbiota of oral iron-treated patients shows higher abundances of the orders Clostridiales, Cytophagales and Anaeroplasmatales compared to intravenous iron-treated patients. The on-tumour microbiota was enriched with the orders Lactobacillales and Alteromonadales in the oral and intravenous iron groups, respectively. The on- and off-tumour microbiota associated with intravenous iron-treated patients infers increased abundances of enzymes involved in iron sequestration and anti-inflammatory/oncogenic metabolite production, compared to oral iron-treated patients. Paired on- and off-tumour microbiota show large taxonomic differences in intravenous iron-treated patients and limited differences in oral iron-treated patients.Conclusion Oral iron shows a large shift in the off-tumour microbiota, but a more limited change in on-tumour microbiota. The on- and off-tumour microbiota in intravenous iron-treated patients infers a microbiota associated with anti-inflammatory and tumour protective pathways. Suggesting intravenous iron may be a more appropriate therapy to limit adverse microbial outcomes, compared to oral iron.Trial registration: NCT01701310. Registered 21 March 2012, https://clinicaltrials.gov/ct2/show/NCT01701310