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19 saat önce -

The way radiation enters the environment or human body can affect what health outcomes researchers expect to see. Nuclear toxicologists investigate the absorption, distribution, metabolism, and excretion (ADME) of radioactive materials in the environment to understand the exposure risks more fully and better predict resultant health outcomes. All these factors matter when it comes to understanding health harms.
Internal exposures involve radioactive materials that directly enter the body during decay and can produce new radioactive decay products within the body. There are several types of internal exposure:
External exposures involve radiation near or around the body that is absorbed and can then affect normal bodily functions. External exposures do not create decay products in the body because the compound itself is not absorbed, just the radiation. External exposures can occur as a result of simply being near radioactive materials without any direct contact.The impacts of internal and external exposures will differ. For example, a uranium miner inhaling uranium that decays into other products within the lung (internal exposure) will experience different health effects than an atomic worker standing near radioactive waste and absorbing the radioactive particles being emitted (external exposure).
Though the air, clothing, and skin generally protect the body from certain types of radiation, they are not a defense against gamma rays emitted by radioactive materials. Gamma radiation is released in large quantities during nuclear weapon detonations or testing, but there are also naturally occurring gamma ray emitters such as americium-241, cesium-137, and cobalt-60, which are used in leveling gauges, smoke detectors, and medical equipment.
The distribution of radiation throughout the body, whether in a target organ or more systemically (e.g., circulating blood), can harm the human body through genetic alterations, tissue and organ damage, or by disrupting normal bodily functions. Radioisotopes can also be distributed and stored in multiple target organs.
There are many target organs for radioisotopes, including bones, teeth, fat cells, the thyroid gland, liver, kidneys, the reproductive system, and breast tissue . The decay of uranium-238 creates many radioactive products such as thorium-234 and -230, radium-226, radon-222, and polonium-218 and -214. Each of these products target different organs: thorium-230 is predominantly stored in bone, but polonium is distributed in soft tissue and bone, and radium is stored on the surface and the marrow of bones. All are decay products of each other that target different areas of the body.
This study found children born in the mid-1960s had levels of strontium contamination 60 times higher than those born in the early 1950s (a 100-fold increase). This work was conducted across the greater St. Louis area by the Committee for Nuclear Information and Washington University faculty. Researchers measured strontium-90 in more than 320,000 baby teeth over a dozen years. Strontium-90 is more easily measured in children due to their increased radiosensitivity and can therefore be measured in bones and teeth (which strontium-90 targets) without having to do something invasive like taking blood or a bone biopsy.
The high levels of strontium-90 in this population have been attributed to radioactive fallout from aboveground nuclear testing. This region has also experienced increased incidence of low birth weights and childhood cancers among people living there.
It is important to understand that some radioactive materials, such as uranium, cause both radioactive harms (such as tissue scarring and alterations to genetic material that can induce cancers) and chemical harms. As a heavy metal, uranium is part of a group of chemicals known to harm neurological function, child development, and birthing outcomes.
Excretion refers to how these harmful materials are removed either from circulation (stored in t

1 gün önce -

We prove that the entanglement entropy of the ground state of a locally gapped frustration-free 2D lattice spin system satisfies an area law with respect to a vertical bipartition of the lattice into left and right regions. We first establish that the ground state projector of any locally gapped frustration-free 1D spin system can be approximated to within error ϵ by a degree O(sqrt{nlog(1/ϵ)}) multivariate polynomial in the interaction terms of the Hamiltonian. This generalizes the optimal bound on the approximate degree of the boolean AND function, which corresponds to the special case of commuting Hamiltonian terms. For 2D spin systems we then construct an approximate ground state projector (AGSP) that employs the optimal 1D approximation in the vicinity of the boundary of the bipartition of interest. This AGSP has sufficiently low entanglement and error to establish the area law using a known technique.
The No Low-energy Trivial States (NLTS) conjecture of Freedman and Hastings, 2014 -- which posits the existence of a local Hamiltonian with a super-constant quantum circuit lower bound on the complexity of all low-energy states -- identifies a fundamental obstacle to the resolution of the quantum PCP conjecture. In this work, we provide new techniques, based on entropic and local indistinguishability arguments, that prove circuit lower bounds for all the low-energy states of local Hamiltonians arising from quantum error-correcting codes. For local Hamiltonians arising from nearly linear-rate or nearly linear-distance LDPC stabilizer codes, we prove super-constant circuit lower bounds for the complexity of all states of energy n). Such codes are known to exist and are not necessarily locally testable, a property previously suspected to be essential for the NLTS conjecture. Curiously, such codes can also be constructed on a two-dimensional lattice, showing that low-depth states cannot accurately approximate the ground-energy even in physically relevant systems.
Ground-state entanglement governs various properties of quantum many-body systems at low temperatures and is the key to understanding gapped quantum phases of matter. Here we identify a structural property of entanglement in the ground state of gapped local Hamiltonians. This property is captured using a quantum information quantity known as the entanglement spread, which measures the difference between Rnyi entanglement entropies. Our main result shows that gapped ground states possess limited entanglement spread across any partition of the system, exhibiting an area-law scaling. Our result applies to systems with interactions described by any graph, but we obtain an improved bound for the special case of lattices. These interaction graphs include cases where entanglement entropy is known not to satisfy an area law. We achieve our results first by connecting the ground-state entanglement to the communication complexity of testing bipartite entangled states and then devising a communication scheme for testing ground states using recently developed quantum algorithms for Hamiltonian simulation.
As small quantum computers are becoming available on different physical platforms, a benchmarking task known as cross-platform verification has been proposed that aims to estimate the fidelity of states prepared on two quantum computers. This task is fundamentally distributed, as no quantum communication can be performed between the two physical platforms due to hardware constraints, which prohibits a joint SWAP test. In this paper we settle the sample complexity of this task across all measurement and communication settings. The essence of the task, which we call distributed quantum inner product estimation, involves two players Alice and Bob who have k copies of unknown states rho, sigma (acting on a d dimensional Hilbert space) respectively. Their goal is to estimate Tr(rho sigma) up to additive error eps, using local quantum operations and classical communication. In th

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