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PSF

The Python Software Foundation (PSF) is a 501(c)(3) non-profit organization founded in 2001 to promote, protect, and advance the open-source Python programming language while fostering its international community of developers. The PSF stewards Python's intellectual property rights, ensures its free global distribution, and supports core implementation efforts including the CPython reference interpreter through dedicated staff and resources. It organizes flagship events like PyCon US, administers the (PyPI) for software distribution, and awards grants—distributing over $655,000 USD in 2024 to 257 projects across 61 countries—to bolster community initiatives in education, diversity, and application development. Under PSF oversight, has achieved preeminence as the most popular programming language on platforms like , driving innovations in , , web frameworks, and scientific research due to its readability, extensibility, and ecosystem of libraries.

Measurement Units

Pounds per Square Foot

Pounds per square foot (psf) is an unit of defined as the force of one pound-force exerted over an area of one . This unit arises from the system's combination of force in pounds and area in , where P = F / A, with F in lbf and A in ft². It is directly related to pounds per (psi) by a factor of 144, since one equals 144 . In the International System of Units (SI), 1 psf equals approximately 47.8803 pascals (Pa), where 1 Pa = 1 N/m². This conversion derives from the definitions: 1 lbf ≈ 4.44822 N and 1 ft² = 0.092903 m², yielding $1 \, \text{psf} = \frac{4.44822}{0.092903} \approx 47.8803 \, \text{Pa}. Psf is primarily used in countries employing imperial or customary units, such as the United States, for applications requiring lower pressure ranges compared to psi. The unit finds extensive application in and , particularly for specifying distributed loads on structures like floors, roofs, and walls. For instance, building codes often mandate minimum live load capacities, such as 40 psf for residential floors or 100 psf for office spaces, to ensure structural safety under occupancy and movable loads. In HVAC systems, psf measures in ducts, aiding design for airflow resistance. It also appears in for soil bearing capacities and in for calculations. These uses emphasize psf's role in practical, low-to-moderate pressure scenarios where measurements persist despite SI adoption elsewhere.

Other Units

In addition to pounds per square foot (psf), pressure measurements in imperial units often employ pounds per square inch (psi), where 1 psi equals exactly 144 psf due to the 144 square inches in a square foot. This conversion is standard in engineering applications like and . The SI equivalent unit is the pascal (Pa), defined as one newton per square meter; 1 psf converts to 47.8803 Pa, facilitating international comparisons in scientific and technical contexts. Other related imperial units include ounces-force per square inch (ozf/in²) and inches of water column (inH₂O at standard conditions), though direct conversions from psf vary with temperature and gravity assumptions, typically requiring hydrostatic principles for precision. For higher pressures, such as in , kilopounds per square foot (ksf) is used, where 1 ksf = 1,000 psf, scaling psf values for loads like bearing capacities. Conversions to or atmospheres are less common for psf-scale applications but follow from Pa equivalents, with 1 ≈ 2,088.54 psf.
UnitConversion Factor to psfExample Application
1 = 144 psfHydraulic systems, pressure
1 ≈ 0.020885 psfScientific
inH₂O (at 4°C)1 inH₂O ≈ 5.202 psfHVAC duct testing
ksf1 ksf = 1,000 psf design loads

Science and Technology

Optics and Imaging

The (PSF) quantifies the blurring effect in an by describing the distribution of from an idealized , such as a or sub-resolution fluorescent bead, in the . This response arises primarily from , as governed by wave , and is exacerbated by aberrations, , and other imperfections in the optical train. For a with a circular , the PSF manifests as the Airy pattern: a central disk of radius $1.22 \lambda f / D (where [\lambda](/page/Lambda) is the , f the , and D the ), encircled by fading concentric rings containing about 84% of the total within the central disk. Aberrations distort this ideal form, broadening the PSF and degrading , which is fundamentally limited by the (FWHM) of the PSF, typically on the order of \lambda / (2 \mathrm{NA}) in , where NA denotes . In microscopy, the three-dimensional PSF captures axial and lateral blurring from out-of-focus light, enabling techniques like to computationally reverse convolution with the observed image, thereby sharpening features beyond the raw limit while suppressing amplification via regularization methods such as filtering. Experimental PSFs are acquired by isolated fluorescent nanobeads (e.g., 100-200 nm diameter) under matched illumination and detection conditions, with subsequent fitting to models like Gaussian or vectorial integrals for precise characterization. In astronomy, the PSF incorporates atmospheric seeing, which can expand the effective FWHM to arcseconds, prompting (AO) systems to deploy deformable mirrors and sensors for real-time correction, yielding Strehl ratios (peak intensity relative to ideal) exceeding 0.5 in near-infrared for large telescopes like the Keck Observatory. AO-corrected PSFs vary temporally and anisoplanatically across the field, necessitating estimation from telemetry data via or parametric fitting to enable high-fidelity and . Advanced computation of PSFs employs , propagating the pupil function (complex amplitude transmittance) through angular spectrum methods or Z-transforms to simulate vectorial effects in high-NA systems, outperforming scalar approximations by accounting for polarization-dependent . Knife-edge scanning or transforms on edge responses provide empirical PSFs without point sources, useful for validating models . These tools underpin super-resolution modalities, where engineered PSFs (e.g., via phase masks) localize emitters to nanometer precision, as in STED or techniques, though practical limits persist from photon noise and sample-induced aberrations.

Computing and Software

The Python Software Foundation (PSF) is a non-profit organization incorporated in Delaware, United States, in 2001, tasked with promoting, protecting, and advancing the Python programming language while supporting its global developer community. As the steward of Python's intellectual property, the PSF manages open-source licensing for Python versions 2.1 and later, holds trademarks such as the "Python" name and "PyCon" for programming-related contexts, and ensures the language's free distribution via official channels. Its governance includes a board of directors elected by members—comprising individuals and sponsors—with monthly meetings and an annual in-person assembly at PyCon North America. The PSF's core activities focus on sustaining Python's ecosystem through infrastructure maintenance, such as operating the (PyPI) for software distribution, and enforcing the community to maintain collaborative standards. It employs a full-time Developer in Residence to aid core implementation efforts and fiscally sponsors over 20 groups, including PyLadies, to enhance diversity and outreach. Funding supports these operations via PyCon fees, corporate sponsorships, and donations, qualifying for U.S. tax-deductible status as a 501(c)(3) entity; historical data shows revenues like $168,000 in 2006 primarily allocated to conferences and grants. A key initiative is organizing PyCon US, the longest-running annual Python-focused conference, alongside grants for global events, projects, and user groups to foster innovation and accessibility. In 2024, the PSF distributed $655,000 D to 257 recipients in 61 countries, building on precedents like $40,000 in grants awarded in 2004 and $33,000 to 18 conferences across 15 countries in 2012. These efforts underscore the foundation's role in enabling Python's widespread adoption in without direct control over the language's technical direction, which remains community-driven.

Chemistry and Materials

Polysulfone (PSF), also denoted as PSU, is an amorphous distinguished by its main chain composition of aromatic rings linked by sulfonyl groups and bonds, conferring inherent rigidity and resilience. This structure enables PSF to maintain structural integrity under elevated temperatures, with a temperature of 187°C and continuous use up to 160°C, alongside low water absorption and resistance to and many chemicals. Its properties include high tensile strength and toughness, making it suitable for demanding applications without significant degradation. In , PSF's processability via methods like phase inversion supports the production of porous membranes and fibers, leveraging its commercial availability and anti-compaction behavior. These attributes position PSF as a preferred material for systems, where its resists degradation from aggressive solvents and oxidants encountered in and gas separation processes. Additionally, PSF's transparency in its form, combined with non-toxicity and sterilizability, facilitates its use in laboratory equipment such as tubes and devices, enduring autoclaving cycles without brittleness. However, PSF's hydrophobic nature limits wettability in aqueous applications, often requiring blend modifications or surface functionalization—such as with hydrophilic additives—to improve and antifouling properties in membrane-based . Research into tailored PSF composites, including those incorporating nanoparticles, has demonstrated enhanced and selectivity, as seen in hollow fiber supports achieving ultrahigh rates exceeding 1000 L/m²·h·bar under optimized spinning conditions. These advancements underscore PSF's versatility, though scalability and cost remain factors in industrial adoption compared to alternatives like polyethersulfone.

Other Scientific and Technical Concepts

In , the photon strength function (PSF) describes the average probability per unit energy interval for the absorption or emission of a in transitions, serving as a key input for statistical models of electromagnetic decay cascades. This function is typically parameterized using shapes for electric dipole (E1) transitions, with refinements accounting for low-energy behaviors and giant resonances, as observed in experiments like reactions. PSFs are derived from on level densities and ground-state transitions, enabling predictions of radiative capture cross-sections and ratios in heavy nuclei. Empirical PSFs often exhibit upbends at low energies (below 6 MeV), challenging theoretical models like the Hartree-Fock-Bogoliubov approach, and are validated through comparisons with Oslo-method extractions from (p,d') reactions. In molecular biology, PSF denotes PTB-associated splicing factor (also known as NONO or p54^{nrb}), a 54-kDa ubiquitously expressed nuclear protein that binds RNA and DNA to regulate alternative pre-mRNA splicing, transcriptional activation, and genomic stability. PSF forms heterodimers with NONO and interacts with RNA polymerase II, facilitating spliceosome assembly at polypyrimidine tract elements and influencing exon inclusion in genes like fibronectin. It also participates in DNA double-strand break repair via non-homologous end joining, with depletion studies showing impaired V(D)J recombination in cell lines. Structurally, PSF contains RNA recognition motifs and a C-terminal domain for protein interactions, and its dysregulation is linked to amyotrophic lateral sclerosis through mutations affecting paraspeckle formation. Experimental evidence from knockout models confirms PSF's essential role, as homozygous disruption leads to early embryonic lethality in mice by E7.5.

Organizations

Political Parties and Movements

The Parti Social Français (PSF) was a conservative nationalist in , established on July 11, 1936, by following the dissolution of the veterans' league by the government. The party emphasized social solidarity, , , and national unity against perceived divisive threats like and parliamentary instability, drawing on social Catholic principles and rejecting both and . While exhibiting authoritarian traits—such as hierarchical organization and paramilitary-style discipline—its ideology aligned more closely with than , as La Rocque distanced the movement from totalitarian models. By 1937, the PSF achieved peak membership of approximately 1.2 million, including significant female participation that transformed it into a mass party with social action programs for women and families; it remains the largest political organization in French interwar history by . The party contested elections with limited parliamentary success, focusing instead on street mobilization and exacerbating France's democratic crisis through confrontational tactics against left-wing governments, before being suppressed in 1940 amid the German occupation. The Parti Socialiste sans Frontières (PSF), also known as the , is a democratic socialist opposition party in advocating , measures, and grassroots governance reforms. Founded as part of the broader opposition to the Déby regime, it joined coalitions like the (FACT) to challenge ruling power structures. On February 28, 2024, party president Yaya Dillo Djerou was killed by Chadian security forces during a on PSF headquarters in , shortly before a planned presidential election, an incident described as an amid allegations of electoral manipulation. The party has since faced ongoing repression, including the arrest of at least 24 militants in the (many released by December 2024), the and subsequent of secretary general Robert Gam in September 2024 after eight months in detention, and the deactivation of its official social media page in 2025. The Parti Socialiste Français of 1902 was a short-lived socialist formation resulting from the merger of Marxist and Blanquist factions, including Jules Guesde's French Workers' Party and Édouard Vaillant's Revolutionary Socialist Workers' Party, during a congress in Commentry. It sought to unify revolutionary socialists opposed to reformist tendencies but fragmented amid ideological disputes, contributing to the later creation of the Section Française de l'Internationale Ouvrière (SFIO) in 1905. In , the People's Students Federation (PSF) operates as the student wing and political movement affiliated with the (PPP), established in 1978 to mobilize youth for socialist-leaning causes, , and opposition to ; it has been involved in campus activism and electoral support but functions as a federation rather than an independent party.

Law Enforcement and Security

The Public Security Forces (PSF) serve as the principal under Bahrain's Ministry of the Interior, responsible for routine policing, traffic control, and public order maintenance. Established as the successor to the Bahrain State Police, the PSF handles day-to-day security operations and has been involved in managing civil unrest, including during protests. In April 2025, Bahrain announced plans to restructure and rename the PSF as the Bahrain Police to modernize its framework and enhance operational efficiency. The Palestinian Preventive Security Force (PSF), also known as the Preventive Security Service, functions as an internal intelligence and agency within the Palestinian Authority's security apparatus. Formed in 1994 under , it operates primarily in plainclothes with an estimated strength of around 5,000 personnel, focusing on preventive measures against threats to internal stability, including investigations and arrests related to security cases. The force holds powers and has collaborated internationally on efforts, though it has faced criticism for involvement in political detentions. The (PSF) is an elite unit established in 2004 by the regional government in to combat insurgent groups such as affiliates. Trained with international support, including from the , the PSF conducts operations against and in the region, though it has experienced internal factional clashes that disrupted its focus on external threats. As of 2022, the force maintained active deployments in key areas like , emphasizing maritime and border security.

Business and Companies

Professional services firms (PSFs) are entities that specialize in delivering advisory, consulting, or technical services grounded in the professional expertise of licensed or highly trained individuals, such as lawyers, accountants, engineers, architects, and consultants. These organizations prioritize over physical assets, with operations often centered on partnerships or similar structures that incentivize sharing and client-focused delivery. Revenue models typically involve hourly billing, fixed-fee projects, or performance-based arrangements, distinguishing PSFs from product-oriented companies. PSFs face distinct operational dynamics, including high reliance on talent acquisition and retention, where employee utilization rates directly impact profitability—often measured through metrics like (the ratio of junior to senior staff) and realization (actual fees collected versus standard rates). Research highlights that effective PSFs maintain tight alignment between client needs and internal capabilities, avoiding diversification into commoditized services that erode margins. For example, amid post-2020 market shifts, many PSFs adapted by emphasizing consulting and data-driven advisory to sustain growth. In commercial , a key business sector, PSF refers to "per ," a pricing convention used to standardize rates, values, and operating costs across . This metric enables apples-to-apples comparisons; for instance, national U.S. averages in 2024 included $37 PSF for spaces, $23 PSF for , and under $20 PSF for industrial facilities, varying by location and . frequently quote base in PSF terms (e.g., $25 PSF annually), with additional pass-through expenses like taxes and calculated separately under structures such as triple net (NNN).

Non-Profit and Foundations

The Python Software Foundation (PSF) is a 501(c)(3) non-profit organization incorporated in Delaware, USA, in 2001, dedicated to promoting, protecting, and advancing the Python programming language while supporting the growth of its international programmer community. The foundation holds the intellectual property rights to Python and fulfills its mission through core activities including grant distribution, fiscal sponsorship of related projects, organization of conferences, and maintenance of community infrastructure. Since launching its grants program in 2015, the PSF has disbursed over $3 million USD to fund -related development, educational initiatives, events, and technology projects worldwide. In 2024 alone, it awarded $655,000 USD to 257 groups and individuals across 61 countries, prioritizing in geographic and contributor representation. These grants support sprints, workshops, documentation efforts, and outreach to underrepresented communities in programming, with applications evaluated based on alignment with Python's ecosystem advancement. The PSF also serves as a fiscal for unaffiliated open-source projects tied to , providing legal and financial oversight without direct control, which enables tax-deductible donations to those efforts. Funding for PSF operations derives primarily from corporate sponsorships, individual memberships, and donations, enabling it to remain independent from any single commercial entity while sustaining 's open-source status. Public records of its finances and board decisions are maintained transparently to ensure accountability. Other entities using the PSF acronym include the Plastic Surgery Foundation, a non-profit funding and education in since 2007, and the Proteus Syndrome Foundation, established to support research and patient services for the rare . These operate in distinct domains from the Python-focused organization and lack overlap in mission or activities.

Other Uses

Medical and Health

Posterior spinal fusion (PSF) is a surgical in which vertebrae are fused along the posterior aspect of the to achieve stability, typically involving the placement of grafts and instrumentation such as pedicle screws and rods. This approach accesses the through an incision in the back, allowing surgeons to decorticate surfaces and apply autografts, allografts, or synthetic substitutes to promote osseous union between adjacent vertebrae. PSF is commonly performed for conditions including , , spinal instability, and deformities such as or , where non-surgical interventions like or bracing have failed. Indications for PSF often include chronic radiating to the legs (), neurological deficits from nerve compression, or progressive in adolescents and adults. For instance, in adolescent idiopathic with curves exceeding 45-50 degrees, PSF serves as a standard intervention to halt progression and restore alignment, though alternatives like vertebral body tethering are emerging for select cases to preserve motion. Patient selection emphasizes factors like bone quality, comorbidities, and curve flexibility, with preoperative imaging such as MRI or confirming the need for fusion levels. The procedure typically lasts 3-6 hours depending on the number of levels fused, with patients under general anesthesia; intraoperative neuromonitoring minimizes risks to neural structures. Bone graft is placed laterally along the transverse processes or , secured by metal hardware to immobilize the segment during healing, which requires 3-6 months for solid . Postoperative care involves bracing, , and gradual , with fusion success rates reported at 85-95% in applications when assessed via imaging at 12 months. Complications of PSF include (1-5% incidence), hardware failure, pseudarthrosis (non-union, 5-10%), and adjacent segment degeneration, though lateral interbody approaches combined with PSF may reduce pseudarthrosis rates and improve sagittal alignment restoration. Long-term outcomes show significant pain reduction and functional improvement in 70-80% of patients with degenerative conditions, but fusion eliminates segmental motion, potentially accelerating wear on adjacent levels. from studies supports PSF's over non-operative management for , though randomized trials are limited due to ethical constraints.

Media and Culture

Progressive segmented frame (PsF), also denoted as PSF, is a video scanning format that enables the transmission and storage of progressive scan content through interlaced channels and media. In this scheme, a single progressive frame is divided into two fields, where the first field comprises all odd-numbered lines and the second field all even-numbered lines, both derived from the identical temporal instant, distinguishing it from true interlaced scanning where fields capture temporally offset exposures. This approach preserves the full vertical resolution and temporal coherence of progressive video while leveraging existing interlaced infrastructure, such as HD-SDI interfaces and tape formats like HDCAM. PsF emerged as a transitional technology during the adoption of (HDTV) standards, particularly to accommodate frame rates like 24p (common in ) or 25p/30p within broadcast systems originally designed for interlaced signals at 50i or 60i. Standardized in Recommendation BT.709, which outlines parameters for HDTV and international program exchange, PsF transport applies to captured pictures at frame rates of 30 Hz or lower, allowing compatibility with interlaced equipment without introducing motion artifacts like combing seen in mismatched progressive-to-interlaced conversions. The (EBU) further describes PsF as splitting frames into alternate-line fields for interlaced transmission, facilitating seamless handling in workflows where sources meet legacy distribution networks. In television broadcasting and post-production, PsF has been employed to distribute cinema-originated content, such as 24 fps material telecined for PAL or systems, by segmenting frames to mimic interlaced fields while maintaining integrity upon de-segmentation at the receiver. For instance, 1080p25 can be transmitted as 1080i50 PsF, ensuring compatibility with monitors and recorders that process interlaced signals, though proper flagging (e.g., via timecode or ID) is required to signal the format and avoid erroneous de-interlacing. This format gained prominence in the early HD transition, appearing in camera outputs (e.g., and models) and formats like , but its use has declined with the proliferation of native interfaces and IP-based workflows that eliminate the need for segmentation. Despite its utility in bridging analog-era constraints, PsF introduces potential compatibility issues if equipment fails to recognize the segmented structure, leading to doubled fields or artifacts on interlaced displays; standards recommend explicit identification in ancillary data packets for 1125-line systems. In cultural contexts, PsF has influenced the quality of televised film content, reducing visible interlacing defects in broadcasts of movies and enabling higher-fidelity archiving of progressive originals on interlaced media, though modern streaming and 4K/8K progressive standards have largely supplanted it.

Miscellaneous

In construction and engineering, PSF (or psf) denotes pounds per square foot, a unit of pressure or distributed load equivalent to approximately 47.88 pascals, used to quantify forces such as snow loads on roofs or floor capacities, with standard atmospheric pressure at sea level measuring about 2116 psf. In real estate and property valuation, PSF stands for per square foot, expressing metrics like rental rates or sale prices relative to building area; for instance, commercial leases are often quoted at specific dollar amounts PSF, facilitating comparisons across properties of varying sizes. Less commonly, PSF refers to proximal stop flow pressure in certain physiological or contexts, though this usage is specialized and not widely standardized outside niche applications.

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