We prove that a perfect square table with four legs, placed on continuous irregular ground with a local slope of at most 15 degrees can be put into equilibrium on the ground by a " rotation " of less than 90 degrees. We also discuss the case of non-square tables and make the conjecture that equilibrium can be found if the four feet lie on a circle.

We prove that a perfect square table with four legs, placed on continuous irregular ground with a local slope of at most 14.4 degrees and later 35 degrees, can be put into equilibrium on the ground by a " rotation " of less than 90 degrees. We also discuss the case of non-square tables and make the conjecture that equilibrium can be found if the four feet lie on a circle.

We prove that a perfect square table with four legs, placed on continuous irregular ground with a local slope of at most 15 degrees can be put into equilibrium on the ground by a " rotation " of less than 90 degrees. We also discuss the case of non-square tables and make the conjecture that equilibrium can be found if the four feet lie on a circle.

We prove that a perfect square table with four legs, placed on continuous irregular ground with a local slope of at most 14.4 degrees and later 35 degrees, can be put into equilibrium on the ground by a " rotation " of less than 90 degrees. We also discuss the case of non-square tables and make the conjecture that equilibrium can be found if the four feet lie on a circle.

[1] We use an ensemble of satellite (MODIS), aircraft, and ground‐based aerosol observations during the ICARTT field campaign over eastern North America in summer 2004 to (1) examine the consistency between different aerosol measurements, (2) evaluate a new retrieval of aerosol optical depths (AODs) and inferred surface aerosol concentrations (PM2.5) from the MODIS satellite instrument, and (3)...

Skidding by means of heavy forestry machinery can affect soil physical properties. We assessed the effects of ground based skidding on soil bulk density and total porosity under the Iranian mountainous forest conditions. Treatments included a combination of four levels of traffic intensity (1, 3, 6, and 15 passes) of a Timberjack 450C rubber skidder and two levels of slope (<20% and >20%). The ...

plant diversityis essential to maintain the health of planet's ecosystems. conservation of biodiversity is necessary for the ecological stability and productivity in natural ecosystems. the aim of this research was to study the biodiversity and richness of plant species (including trees, shrubs and grasses) related to the environmental factors (soil and physiography) in the forests of zagros, w...

A filtering algorithm is proposed that accurately extracts ground data from airborne light detection and ranging (LiDAR) measurements and generates an estimated digital terrain model (DTM). The proposed algorithm utilizes planar surface features and connectivity with locally lowest points to improve the extraction of ground points (GPs). A slope parameter used in the proposed algorithm is updat...