Optical data transfer permits much higher data rates and ranges than current electronic processes while also using less energy. Computation and data centres, therefore, already default to optical fiber whenever cables exceed a length of about one metre. In future, optic solutions will be in demand for shorter and shorter distances due to increasing requirements, for example board to board or chip to chip data transfer. This applies particularly to artificial intelligence (AI) systems where large data volumes must be transferred within a large network in order to train the chip and the algorithms.

“The most crucial missing component is a cheap laser, which is necessary to achieve high data rates. An electrically pumped laser compatible with the silicon-based CMOS technology would be ideal,” explains Prof. Detlev Grützmacher, director at Forschungszentrum Jülich’s Peter Grünberg Institute (PGI-9). “Such a laser could then simply be shaped during the chip manufacturing process since the entire chip production is ultimately based on this technology.”

But there is one problem: pure silicon is an “indirect semiconductor” and, therefore, unsuitable as a laser material. Different materials are currently used for manufacturing lasers. Generally, III-V compound semiconductors are used instead. “Their crystal lattice, however, has a completely different structure than that of silicon, which is a group IV element. Laser components are currently manufactured externally and must be integrated subsequently, which makes the technology expensive,” explains Grützmacher.

In contrast, the new laser can be manufactured during the CMOS production process. It is based on germanium and tin, two group IV elements like silicon. Back in 2015, Jülich researchers showed that laser emission can be obtained in GeSn system. The decisive factor in this is the high tin content: back then, it amounted to 12 %, which is far above the solubility limit of 1 % .

“Pure germanium is, by its nature, an indirect semiconductor like silicon. The high concentration of tin is what turns it into a direct semiconductor for a laser source,” explains Dr. Dan Buca, working group leader at Jülich’s Peter Grünberg Institute (PGI-9).

The patented epitaxial growth process developed by Jülich is used by several research groups all over the world. By further increasing the tin concentration, lasers have already been made that work not only at low temperatures but also at 0°C.

“A high tin content, however, decreases the laser efficiency. The laser then requires a relatively high pumping power. At 12-14 % tin, we already need 100-300 kW/cm2,” explains Nils von den Driesch. “We thus tried to reduce the concentration of tin and compensate this by additionally stressing the material, which considerably improves the optical properties.”

For the new laser, the researchers reduced the tin content to approximately 5 % — and simultaneously decreased the necessary pumping power to 0.8 kW/cm2. This produces so little waste heat that this laser is the first group IV semiconductor laser that can be operated not only in a pulsed regime but also in a continuous working regime, i.e. as a “continuous-wave laser.”

“These values demonstrate that a germanium-tin laser is technologically feasible and that its efficiency matches that of conventional III-V semiconductor lasers grown on Si. This also brings much closer to an electrical pumped laser for industrial-application that works at room temperature,” explains institute head Grützmacher. The new laser is currently limited to optical excitation and low temperatures of about -140°C.

Such a laser would be interesting not only for optical data transfer but also for a variety of other applications since there are hardly any cheap alternatives for the corresponding wavelengths in the infrared range of 2-4 ?m. Potential applications range from infrared and night-vision systems all the way to gas sensors for monitoring the environment in climate research or even breath gases analyses for medical diagnosis.

The scalable, automated system uses content-based image retrieval and applies computer vision-based techniques to root out political memes from multiple social networks.

“Memes are easy to create and even easier to share,” said Tim Weninger, associate professor in the Department of Computer Science and Engineering at Notre Dame. “When it comes to political memes, these can be used to help get out the vote, but they can also be used to spread inaccurate information and cause harm.”

Weninger, along with Walter Scheirer, an assistant professor in the Department of Computer Science and Engineering at Notre Dame, and members of the research team collected more than two million images and content from various sources on Twitter and Instagram related to the 2019 general election in Indonesia. The results of that election, in which the left-leaning, centrist incumbent garnered a majority vote over the conservative, populist candidate, sparked a wave of violent protests that left eight people dead and hundreds injured. Their study found both spontaneous and coordinated campaigns with the intent to influence the election and incite violence.

Those campaigns consisted of manipulated images exhibiting false claims and misrepresentation of incidents, logos belonging to legitimate news sources being used on fabricated news stories and memes created with the intent to provoke citizens and supporters of both parties.

While the ramifications of such campaigns were evident in the case of the Indonesian general election, the threat to democratic elections in the West already exists. The research team at Notre Dame, comprised of digital forensics experts and specialists in peace studies, said they are developing the system to flag manipulated content to prevent violence, and to warn journalists or election monitors of potential threats in real time.

The system, which is in the research and development phase, would be scalable to provide users with tailored options for monitoring content. While many challenges remain, such as determining an optimal means of scaling up data ingestion and processing for quick turnaround, Scheirer said the system is currently being evaluated for transition to operational use.

Development is not too far behind when it comes to the possibility of monitoring the 2020 general election in the United States, he said, and their team is already collecting relevant data.

“The disinformation age is here,” said Scheirer. “A deepfake replacing actors in a popular film might seem fun and lighthearted but imagine a video or a meme created for the sole purpose of pitting one world leader against another — saying words they didn’t actually say. Imagine how quickly that content could be shared and spread across platforms. Consider the consequences of those actions.”

Story Source:

Materials provided by University of Notre Dame. Original written by Jessica Sieff. Note: Content may be edited for style and length.

These carefully planned experiments produced cracked concrete slabs and contorted steel beams, but from the rubble arose a wealth of new insights into how real-world structures behave and can eventually fail in uncontrolled building fires. The results of the study, reported in the Journal of Structural Engineering, indicate that structures built to code are not always equipped to survive the forces induced by extreme shifts in temperature, but the data gained here could help researchers develop and validate new design tools and building codes that bolster fire safety.

In the United States, fireproofing materials are sprayed or painted onto weight-bearing beams or columns to slow their temperature rise in case of a fire. These materials, which are typically the only fire-resistance measures integrated into the skeletons of buildings, are required by building codes to be thick enough to delay structural deterioration for a certain number of hours. The responsibility of putting fires out or preventing them from spreading, however, typically falls on measures outside of the structural design, such as sprinkler systems and local fire departments.

The current approach to fire safety is typically sufficient to protect most buildings from collapse; however, there are rare situations in which fire protection systems and firefighting efforts are not enough. In dire circumstances like these, where fires rage in an uncontrolled fashion, flames can sometimes burn so hot that they overwhelm the defense of the fireproofing and seal the structure’s fate.

Just like the red liquid in a thermometer rises on a hot day, components of a building will undergo thermal elongation at elevated temperatures. But whereas the liquid has room to expand, steel beams, like those used to hold up floors in office buildings, are typically bound at their ends to support columns, which typically stay cool and maintain their shape for longer because of additional fireproofing and the reinforcement of the surrounding structure. With very little wiggle room, beams that heat up during fires could press up against their uncompromising boundaries, potentially breaking their connections and causing floors to collapse.

To better prepare buildings for worst-case scenarios, structural designs may need to account for the forces introduced by fires. But because the behavior of a burning building is complex, structural engineers need help predicting how their designs would hold up in an actual fire. Computer models that simulate building fires could provide invaluable guidance, but for those tools to be effective, a considerable amount of experimental data is needed first.

“The main purpose of this experiment is to develop data from realistic structure and fire conditions that can be used for developing or validating computational programs,” said Lisa Choe, NIST structural engineer and lead author of the study. “Then the programs can be expanded to different building configurations and used for design.”

Structures are seldom fire-tested at a realistic scale. Standard tests make use of laboratory furnaces that typically only accommodate individual components or small assemblies without the kinds of end connections that are used in buildings. Size is less of an issue for NIST, however. Within the National Fire Research Laboratory (NFRL), engineers can build and safely burn structures as tall as two stories and have a plethora of tools available to inspect the destruction.

Mimicking the design of floors from high-rise office buildings, Choe and her colleagues at the NFRL formed concrete slabs atop steel beams spanning 12.8 meters (42 feet) — a typical length in office buildings and also the longest fire-tested in the United States. The floors were suspended in the air, fastened at their ends to support columns either by double angle or shear tab connections, which are differently shaped but both commonplace.

To make the test conditions even more true to life, the engineers used a hydraulic system to pull down on the floors, simulating the weight of occupants and moveable objects like furniture. The beams were also coated in fireproofing material with a two-hour fire-resistance rating to meet building code requirements, Choe said.

Inside a fireproof compartment, three natural-gas fueled burners torched the floors from below, releasing heat as rapidly as a real building fire. While the compartment warmed up, various instruments measured the forces felt by the beams along with their deformation and temperature.

As temperatures within the compartment surpassed 1,000 C, the expanding beams, having been constrained between two support columns, began to buckle near their ends.

No floor came out of the fire tests scot-free, but some withstood more than others. After around one hour of heating, the shear tab connections of one beam — now having dipped down by more than two feet — fractured, leading to collapse. The beams with double angle connections, however, beat the heat and remained intact. That is, until they tumbled down hours after the furnaces were shut off, as the beams cooled and contracted back upwards, breaking the double angle connections.

While the study’s small sample size means conclusions about buildings in general could not be drawn, Choe and her team did find that the beams with double angle connections endured greater forces and deformations from the temperature changes than those with shear tab connections.

“The influence of the thermal elongation and contraction is something that we shouldn’t ignore for the design of steel structures exposed to fires. That’s the big message,” Choe said.

Toward the goal of more robust designs, these results provide invaluable data for researchers developing predictive fire models that could lay a foundation for buildings that resist not only burns, but the force of fire.